Micro Fight Chassis Mk4

The Spiritus Systems Micro Fight Chassis Mk4 is the placard footprint that defined the modern modular chest rig category. The chassis itself is just two pockets and a rear hook field, but the Spiritus ecosystem around it — Expander Wings for capacity, LV-119 Plate Bags for armor, the Thing 3 for sustainment loadouts — turns the same $76 footprint into anything from a low-vis range rig to a full plate carrier.

Both interior pockets are lined with soft-loop hook field, which means magazine inserts, sub-gun inserts, pistol inserts, and admin inserts all reindex via VELCRO. Swap the 5.56 insert for a 7.62x51 insert when you grab the AR-10, swap to a single rifle + double pistol layout for a PCC class, swap to admin inserts for low-vis carry. The chassis stays; the loadout adapts.

The Mk4 is sold as the chassis only. Building a usable standalone chest rig adds shoulder straps, a back strap, and at least one magazine insert (budget $200-260 total for a complete configuration). That said, the system pays for itself the first time you want to put your existing mag pouches on a plate carrier — the rear 5x9 hook field maps directly onto every major plate carrier with a hook front panel.

Spiritus drops are routine and color/configuration availability cycles in waves. Out-of-stock is the norm rather than the exception for popular configurations like Multicam and Coyote.