The Spiritus Systems Ecosystem: Every Build Option Explained

Spiritus Systems did not build a chest rig. They built a platform. This guide covers the entire ecosystem: every chassis option, every pouch category, radio integration, medical setup, and exactly how the pieces connect. From a stripped-down low-profile build to a fully loaded comms and medical rig, this is everything the system can do.

The Micro Fight system fully built out — chassis, expander wings, pouches, radio, sub-abdominal layer

Most chest rigs are a fixed product. You buy what you get and work around the limitations. The Spiritus Systems Micro Fight is different because the chassis is not the end of the conversation. It is the beginning. Every component in the Spiritus lineup is designed to connect to something else, and the resulting build options range from a minimalist pistol-mag placard under a jacket to a full comms, medical, and ammunition rig that can run for days in the field.

At Gear Town we carry the full Spiritus range because it is genuinely one of the most complete tactical load-bearing ecosystems available in Europe. This guide walks through every layer of the system so you can make informed decisions about what to build and how to build it.

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1. Choosing Your Chassis

The chassis is the core of the system. Everything else builds around it. Spiritus Systems offers several chassis options, each designed for a specific use case. The right starting point depends on whether you primarily want a standalone chest rig, a plate carrier placard, or a split-front design for use over armour.

Micro Fight Chassis Mk4

The Mk4 is the foundation of the Spiritus lineup and still the most versatile option. It has two separate front pockets, each lined with soft loop on the interior. This means you can configure each pocket independently: rifle inserts in one, pistol inserts in the other, or any combination the mission calls for. The hook field on the back measures 5 by 9 inches and provides solid connection to plate carriers, expander wings, sub-abdominal pouches, and the glove hook. Two integrated grommets at the bottom of the chassis accept the Universal Retention Kit for tourniquet stowage on both sides. The Mk4 is the right choice when you want a capable standalone rig that also works as a placard.

Micro Fight Chassis MkV

The MkV is a single-cell placard-style chassis. Unlike the Mk4, it has a single main compartment rather than two separate pockets, and the front face is covered in MOLLE webbing. This means you can run external pouches directly on the front of the chassis. The main cell is loop-lined on both sides and accepts all Spiritus magazine inserts. Its companion product is the CCS Pouch, which covers the entire front MOLLE face with a clamshell general-purpose storage pouch and transforms the MkV into a highly capable admin and magazine rig. The MkV is also compatible with the Lunchbox Pouch, giving you sub-abdominal medical storage below the chassis.

Micro Fight Chassis Mk6

The Mk6 is the newest iteration of the single-cell placard design and represents the most refined integration with the Spiritus LV-120 plate carrier ecosystem. It connects to the LV-120 via side release buckles, optional Flat G-Hooks, or First Spear Tubes for a cummerbund-locked attachment. The Mk6 is fully UCAS compatible, which means it integrates with a wider range of carrier systems without additional adapters. Height-adjustable rear buckle straps let you fine-tune placement on the carrier. As a standalone rig with Fat Straps attached, the Mk6 is one of the slimmest options in the Micro Fight family, making it the preferred chassis for low-visibility applications.

34 Alpha Split Chest Rig

34 Alpha in Ranger Green — sternum-clear split-front design

The 34 Alpha takes a fundamentally different structural approach. Instead of one central chassis, it uses two separate panels connected via sliding Fastex buckles at the front. Each panel mounts independently to the Fat Strap Mk4. The result is a chest rig with an open sternum area, which significantly reduces stacking height when worn over body armour and allows the front to open with a single motion, something useful during prone work or when transitioning rapidly. Each panel has six columns of MOLLE on the front and internal elastic cells on the back for pistol magazines, multi-tools, and flat-pack items. The 34 Alpha is the system for operators who spend significant time in armour and find centrally-massed rigs uncomfortable or restrictive.

The Thing 3

The Thing 3 — lateral body-worn expansion platform

The Thing 3 is not a chest rig in the traditional sense. It is a torso-worn chassis that sits between your Fat Straps and gives you a large MOLLE and loop mounting surface on both the front and back of the piece. A dedicated loop field and retaining loops at the center accept the Micro Fight MkV, Mk4, or any other brand placard, so your magazine chassis rides on the Thing 3 rather than directly on your chest. This creates separation between your main ammunition load and your body and allows for full articulation. The outer MOLLE surfaces of the Thing 3 can carry SPUD Pouches, GP pouches, the Lunch Box, or the Brunch Box. The Thing 3 requires Fat Straps and a Back Strap and is only available in Coyote Brown and Black.

Placard 5.56 x .45

The Placard 5.56 is the slimmest chassis in the lineup. It is a purpose-built single-caliber magazine placard with no frills and no general-purpose pocket. If your mission calls for magazine access and nothing else on the front of your carrier, the Placard 5.56 delivers the minimum viable footprint. It mounts to a plate carrier front panel or attaches to the Thing 3 via hook and loop. It does not use Fat Straps and cannot be worn as a standalone rig.

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2. The Harness System

Fat Strap Mk4 — the primary suspension component for all standalone Spiritus rigs

Fat Strap Mk4

The Fat Strap Mk4 is the shoulder harness used across the Micro Fight, 34 Alpha, and Thing 3 systems. A single Fat Strap forms a complete H-harness: one continuous strap that runs over both shoulders and connects to the chassis via the side buckle system. The nylon laminate overlay panel runs along the shoulder portion and includes horizontal mounting rails for PTT clips and other electronic accessories. Shock cord holes at intervals allow additional kit to be lashed to the strap without adding external volume. A loop field strip on the rear of the strap allows name tape or IR identification marker attachment. One Fat Strap is all you need for any of the compatible rigs.

Back Strap

The Back Strap is a simple one-inch webbing piece that runs across your upper back and connects the lower buckles of the Fat Strap together, preventing the rig from pulling forward during movement. In addition to its standard role, the Back Strap can be reconfigured as a cross-body sling, which turns the Micro Fight Chassis into a compact go-bag for quick-access carry over the shoulder. Fully adjustable from 8 to 36 inches. Available in Multicam, Ranger Green, Black, and Coyote Brown.

EUD Bridge

EUD Bridge in use — ATAK device mounted centrally on the rig shoulder straps

The EUD Bridge is a mounting platform that attaches to the Fat Strap shoulder straps and suspends an End User Device, typically an ATAK-enabled tablet or smartphone, in the center of the chest between the two shoulder runs. It is built from CURV thermoplastic composite and nylon laminate, creating a rigid and stable mounting surface that absorbs movement without transmitting vibration to the device. The EUD Bridge includes slits for PTT clip routing and an optional mounting plate kit for hard-point attachment of an MPU5 PTT without relying on a factory gator clip. For operators running Android devices for navigation, coordination, or fire support calls, the EUD Bridge puts the screen exactly where it needs to be.

TAPS Upgrade Kit Mk2

TAPS stands for Tourniquet Arm Placement System. The TAPS Upgrade Kit Mk2 converts your Micro Fight chest rig into a rapid tourniquet deployment platform integrated directly into the rig structure. Rather than stowing a tourniquet in a pocket or clipped externally, TAPS positions it on the rig frame for immediate one-handed application. The Mk2 version is compatible with all current Micro Fight chassis versions and adds significantly to the medical readiness of a standalone rig without adding visible bulk.

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3. Ammunition: Magazine Inserts

Rifle Magazine Inserts — triple 5.56 and double 7.62 options in black

The insert system is what makes the Micro Fight genuinely multi-caliber. All inserts attach via the soft loop field inside each pocket, meaning they can be swapped, rearranged, or mixed in any combination. Each insert holds magazines with elastic cells that provide silent extraction, strong retention, and will not deform with heat over time.

Rifle Magazine Inserts

Available in triple 5.56, double 7.62, double HK 417, and single configurations. The triple 5.56 insert is the most common choice for the Mk4, running three magazines per pocket for a total of six across the chassis. The double 7.62 accommodates larger rifle calibers in the same footprint. All rifle inserts fit both PMAG and USGI magazine formats and are available in black only.

Pistol Magazine Inserts

Available in single and double versions. The pistol inserts allow you to dedicate one pocket of the Mk4 to secondary ammunition while the other runs rifle magazines. Running a double pistol insert in the front pocket with a triple 5.56 in the rear is one of the most common mixed-ammunition configurations, particularly for operators who want immediate pistol access without reaching for a belt-mounted holster.

Submachine Gun Magazine Insert

The SMG insert accommodates compact-format magazines for sub-gun platforms. It fits the same pocket dimensions as the rifle inserts and is used primarily by operators running MP5, MPX, or similar platforms where standard rifle insert sizing is not appropriate.

Elastic Magazine Pouch (EMP) and Triple Elastic Magazine Pouch (TEMP)

Triple Elastic Magazine Pouch (TEMP) — MOLLE-mounted, accepts Pangolin Flap

The EMP is a single-pocket MOLLE-mounted elastic magazine holder that mounts to the MOLLE field of the MkV, the Thing 3, cummerbunds, or any MOLLE surface. The TEMP expands on this concept with three side-by-side elastic cells, a bungee retention kit option, and a loop exterior that accepts the Pangolin Flap for closure. The TEMP is particularly popular on the MkV and on cummerbunds as a lateral magazine carrier that complements a slimmer front chassis. It also accepts the standard Pangolin Flap, which wraps around the magazines and secures them during movement without requiring a separate flap system.

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4. Flaps and Retention

Full Flap Mk2

The Full Flap Mk2 is designed for the Mk4 chassis and covers the entire front face of both pockets in a single nylon laminate panel. It attaches via a strip of hook and loop between the magazine insert and the inner wall of the pocket, and folds down over the front of the chassis. A full-width pull tab allows one-handed access. The Full Flap is the preferred option for vehicle operations, extended movement in rough terrain, or any situation where magazines must stay locked in position regardless of orientation.

Half Flap Mk2

The Half Flap Mk2 covers only the upper portion of the front pocket. This allows the lower half of the pocket to remain open, which is useful when running pistol magazine inserts in the lower portion of the pocket alongside rifle magazines up top. The half-coverage design is also the most popular choice for a patrol setup where frequent magazine access is expected but some retention is still needed during movement.

Pangolin Flap

The Pangolin Flap is a per-magazine closure designed for both the Mk4 chassis pockets and third-party magazine pouches that have a loop field on the front. Rather than covering the entire pocket, the Pangolin Flap wraps around each individual magazine using a multi-directional laser-cut scrim pattern that conforms around irregular shapes under tension. Multiple Pangolin Flaps can be run simultaneously across the chassis. They are sold individually. The Sub-Gun Pangolin Flap serves the same function for compact magazine formats.

Bungee Retention Kit

The Bungee Retention Kit consists of bungee cord loops that thread through anchor point holes at the top of the chassis or pouch opening, creating a lightweight retention layer over the magazines without any coverage over the front face. This is the fastest-access retention option in the system and is widely used by competitive shooters or operators in non-permissive environments where rapid magazine changes are the priority.

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5. Going Wider: Expander Wings

Expander Wing Mk2

Expander Wings attach to the soft loop field on the back of the Mk4 chassis and extend outboard on either side of the rig. Each wing is a 6-inch-deep open pocket with an adjustable internal retention strap that can be shortened or lengthened depending on what is carried. Eyelets at the top of each wing accommodate the Bungee Retention Kit so that radios, magazines, or other items stowed in the wing stay secure during movement. The Expander Wing Mk2 is reversible, meaning one wing can run on either the left or right side without modification. Sold individually. Order two for a full set.

In a plate carrier configuration, the Expander Wing Mk2 integrates with the LV-119 cummerbund. A First Spear Tubes bar pass-through allows the cummerbund to attach or separate without removing the wing, preserving full armor integration.

MOLLE Expander Wing

The MOLLE Expander Wing serves a different role from the Mk2 variant. It is a rigid MOLLE platform built on ballistic Tegris material with a double-sided hook and loop attachment and a Two-column, two-row MOLLE grid. It is designed to mount under the cummerbund of the LV-119 or below a Micro Fight Chassis, creating an outboard MOLLE platform for additional pouches that rides closer to the body than the full Mk2 wing. Metal eyelets across the grid allow items to be lashed or zip-tied directly. It also integrates with Tubes cummerbund systems.

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6. Radio and Communications Integration

Radio chassis and comms integration on the Micro Fight platform

The Spiritus ecosystem has a full answer to radio and communications integration. Between the Radio Chassis Mk5, the EUD Bridge, the SPUD Pouch, and the Fat Strap PTT routing, a Micro Fight rig can carry and access every element of a comms suite without resorting to improvised solutions or third-party mounting that compromises the fit of the system.

Multi Platform Radio Chassis Mk5 (MPRC Mk5)

The MPRC Mk5 is a three-part adjustable radio chassis that accommodates an exceptionally wide range of radio models, from compact units like the Motorola XTS 5000 up to full-size platforms like the Persistent Systems MPU5, L3/Harris AN/PRC-163, and Thales AN/PRC-148. The chassis backer is a semi-rigid board that can mount to MOLLE cummerbunds, chest rigs, and packs via two MOLLE columns, or directly to a belt via an integrated pass-through. The base of the system is a tri-flap battery cup that is height-adjustable via MOLLE on the backer, allowing the user to reach the battery compartment without removing the radio from the chassis. A top strap threads through the backer in one of two slots to stabilize radios of different heights without blocking buttons or toggles.

The MPRC Mk5 is most commonly mounted on the Expander Wing outboard of the chassis, on the cummerbund below the arm, or on the back panel in a secondary radio position. Combined with the Fat Strap PTT routing, the system keeps the radio body off the front face of the rig while keeping push-to-talk immediately accessible.

SPUD Pouch

The SPUD Pouch is the dedicated radio pouch in the Spiritus GP pouch family. It mounts via MOLLE and is sized to accommodate most handheld tactical radios in a front-access configuration. The SPUD Pouch can be run on the MOLLE front of the MkV, on Expander Wings, on the Thing 3, or on any MOLLE cummerbund. When combined with the MPRC Mk5 for larger radios or a SPUD Pouch for handheld units, the Micro Fight system can carry two separate radio platforms in a clean, purpose-built configuration.

Mutant Pouch

The Mutant Pouch is a large-format, multi-compartment pouch that works for both radio storage and general purpose applications. It features an articulated opening and an internal organization layer that keeps cables, PTT devices, and radio accessories from tangling. For operators running a full comms suite alongside admin and medical items, the Mutant Pouch is the single-pouch solution that covers the most ground.

Fat Strap PTT Routing

The Fat Strap Mk4 includes horizontal mounting rails along the shoulder overlay panel specifically for PTT clips and cable management. This keeps push-to-talk cables routed cleanly from the radio to the ear, without the cable crossing the front face of the rig or catching on equipment. The loop field on the back of the Fat Strap can secure cable runs using elastic cord through the shock cord holes.

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7. General Purpose Storage

Full chest rig build with general purpose pouches integrated on the platform

CCS Pouch

The CCS Pouch is the purpose-built general purpose solution for the MkV chassis. It attaches via six columns of MOLLE and covers the entire front MOLLE face of the MkV. The CCS has two internal sections: a rear compartment with tie-down loops for utility inserts and a forward pocket for phones, admin items, and tools. Both sections close with double zippers. The exterior has a loop field strip for patches and identification. A tourniquet can be attached below the CCS Pouch using the Universal Retention Kit. When the CCS Pouch is mounted on the MkV, the result is a rig that carries six rifle magazines internally and a substantial volume of general-purpose equipment on the front, all within a compact footprint.

Small GP, Medium GP Mk3, Tall GP, Wide GP

The full Spiritus GP Pouch family covers four size formats: Small, Medium Mk3, Tall, and Wide. All mount via MOLLE and feature the same construction quality as the chassis components. The Medium GP Mk3 is the most commonly chosen size for the outboard position on Expander Wings, where it carries medical equipment, batteries, food, or other mission-specific items. The GP Tall is the preferred option for longer items like bolt cutters or breaching tools that do not fit standard pouch dimensions. All GP Pouches include an external loop field for identification patches.

TKO Pouch

The TKO Pouch is a compact admin-focused pouch with a slim profile that fits neatly between other components on the rig. It is well suited to phone, notebook, map, and ID carry in positions where larger pouches would obstruct access to magazines or other primary equipment.

JSTA Pouch

The JSTA Pouch is a deeper, single-compartment GP pouch designed for items that need easy upward retrieval. It works well for radios, maps, or large admin kits and mounts outboard on Expander Wings or cummerbunds via standard MOLLE.

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8. The Sub-Abdominal Layer

One of the most underused features of the Spiritus platform is the sub-abdominal attachment system. The 5 by 9 inch hook field on the back of the Mk4 connects directly to sub-abdominal pouches that hang below the chassis, using your body's natural abdominal space for additional storage without adding forward profile to the rig. This is how the Micro Fight achieves volume that competes with much larger rigs while keeping the front profile slim.

SACK Pouch Mk3

The SACK Pouch Mk3 is the primary sub-abdominal pouch in the Spiritus lineup. It hangs below the Mk4 chassis via the hook field connection and provides a medium-volume clamshell compartment for medical gear, batteries, food, or mission-specific items. The SACK Pouch Mk3 is also available with a MOLLE-mount version (the MOLLE SACK Pouch) for carrier and Thing 3 integration, and as a Fanny SACK Mk3 with a waist strap for standalone belt carry.

Brunch Box

The Brunch Box is a large-volume sub-abdominal pouch that replaces the SACK Pouch when the mission demands significantly more storage below the chassis. It connects to the same hook field system as the SACK and adds a substantial additional layer of equipment capacity without any forward impact on the rig profile.

Lunchbox Pouch Mk2

The Lunchbox Pouch Mk2 is the medical and utility-optimized sub-abdominal option. Its clamshell opening and internal organization are designed for fast access to medical components, IFAK contents, or compact tool kits. Combined with the TAPS Upgrade or Universal Retention Kit, the Lunchbox creates a sub-abdominal medical layer that keeps critical care equipment off the main rig face without compromising access speed.

The Muff

The Muff is a sub-abdominal handwarmer designed in collaboration with WRMFZY for cold-weather operations. It mounts below the chassis using the same hook and loop tab system and provides an insulated compartment where the wearer can warm hands between tasks. The interior is lined with Polartec Wind Pro and sealed with elastic cuffs. When not in use, The Muff folds and rolls down to a compact package secured by a zipper. It includes a gear pocket for phone, batteries, or small accessories. For winter training environments, The Muff solves the problem of maintaining fine motor skill readiness in extremely cold conditions without sacrificing rig organization.

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9. Medical Integration

The Spiritus platform has three primary medical integration points: the tourniquet grommets on the Mk4 chassis, the TAPS Upgrade Kit, and the sub-abdominal Lunchbox Pouch. Combined with Expander Wings and the Delta Bag for carrier setups, the system can carry a complete trauma kit without dedicating any of the front ammunition space to medical storage.

Universal Retention Kit

The Universal Retention Kit is the standard tourniquet mounting solution for the Micro Fight platform. It threads through the two integrated grommets at the bottom corners of the Mk4 chassis and secures a CAT or similar tourniquet in a compressed, deployment-ready position accessible with either hand. This is a standard inclusion in the full combat build.

TAPS Upgrade Kit Mk2

The TAPS system goes further than the Universal Retention Kit by integrating tourniquet access into the structure of the rig harness itself. This positions the tourniquet in a location optimized for rapid self-application to the arm, which is the most critical and most time-sensitive tourniquet application scenario. The Mk2 kit is compatible with all current Micro Fight chassis versions.

Delta Bag

The Delta Bag is Spiritus Systems' assault medic configuration. It is a compact bag that mounts over a plate carrier and provides three diagonal-access front compartments, a clamshell main compartment with dual loop fields, and two flat rear compartments for keeping items damage-free during carry. The clamshell design allows the Delta Bag to function as a portable workstation when opened flat: integrated handles allow it to be carried between treatment locations without closing the compartments. It is designed for assault medics, team leaders carrying group medical supplies, or any operator who needs immediate access to a complete trauma kit in the field.

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10. Special Setup: Winter Warfare Kit

Winter Warfare Assault Kit — a complete cold-weather chassis configuration

The Winter Warfare Assault Kit is Spiritus Systems' response to a specific operational problem: standard hook-and-loop closures, pull tabs, and Fastex buckle manipulation become unreliable in freezing temperatures when worn with insulated gloves. The Winter Warfare kit reconfigures the Micro Fight platform around these constraints, replacing standard components with winter-specific closures, retention systems, and harness elements designed to function with heavy gloves and reduced dexterity.

The kit includes chassis-specific components and is designed as a complete seasonal swap rather than a modification to an existing build. Operators who run in cold environments rotate between their standard warm-weather build and the Winter Warfare configuration depending on conditions. The Muff sub-abdominal handwarmer pairs with this kit as a companion product.

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11. Five Build Configurations

With the full ecosystem mapped out, here are five concrete configurations that show how the parts come together across the spectrum from maximum capability to minimum footprint.