The T.REX Sidecar is the flagship appendix inside-the-waistband holster — the product around which the entire modular IWB carry concept was built. Where most holsters are static, finished objects, the Sidecar is a platform: a single precision-formed Kydex shell married to an open-source spine system that accepts a growing family of interchangeable attachments. The result is an appendix rig that can be configured as a bare holster, a holster-plus-spare-magazine package, or a holster carrying a tourniquet, rifle magazine, suppressor, or even handcuffs — all without tools beyond a push pin.
The Spine System
The defining feature of the Sidecar is the T.REX Spine System. A machined steel rod runs down the centerline of the holster, with teeth cut at quarter-inch intervals by a standard end mill. Attachments slot onto the spine and are retained by a headless steel pin seated through a rubber friction washer. This pin-and-washer design was chosen after testing cotter pins, clevis pins, ball-retention pins, and shaft collars with set screws. The headless pin eliminates snag points while the friction washer adds rigidity and security — both critical for a holster that rides inside the waistband against skin and clothing all day.
Because each attachment slides along the spine’s notches, the user can adjust mounting height independently of the holster body. Lowering a pistol mag carrier to align the top of an extended magazine flush with the slide, for example, is a matter of repositioning the attachment a notch or two. When the attachment moves, belt clips should be repositioned on their adjustment holes to keep the entire rig riding at the correct height on the belt line.
The spine system is open source. Full blueprints and CAD models are published so that other holster makers, 3D-printing hobbyists, and field experimenters can build compatible attachments from Kydex, Biothane, injection-molded plastic, 3D-printed materials, or even zip ties. This is a deliberate design philosophy: rather than lock users into a closed ecosystem, the Sidecar invites the community to innovate on the platform.
Holster Body and Fit
The holster shell is formed from a single piece of 0.093″ precision-formed Kydex — no seams, no layered panels, no separate sweat guard riveted on. This single-piece construction produces a smooth interior that protects the finish of the pistol and a slim exterior that minimizes printing under a cover garment. The approach reflects a broader conviction that Kydex is the superior material for serious carry holsters: it holds its shape, provides audible and tactile retention feedback, and doesn’t collapse when the pistol is drawn.
Every Sidecar ships optic-cut by default, accommodating any slide-mounted red dot that sits behind the ejection port along with suppressor-height sights up to 0.5″ tall — a nod to the reality that red-dot-equipped carry pistols are now the standard rather than the exception. Frame-mounted optics or those overhanging the ejection port are not compatible.
An adjustable claw on the front of the holster leverages the belt to push the grip into the body, a mechanism central to claw-based concealment. The claw can be repositioned or extended for more or less aggressive tuck depending on body type and cover garment. Two tuckable IWB clips are spaced wide enough to straddle a belt buckle, and each offers 0.5″ of vertical adjustment. Clips are available in high-strength acetal plastic or heat-treated C1050 spring steel with a powder-coat finish, fitting belts from 1.5″ to 1.75″.
Retention is adjusted via screws at the trigger guard or weapon-light interface. A key practical note: retention should always be tested while the holster is worn in the waistband, not on the bench. Compression from the belt and body adds meaningful retention that bench testing cannot replicate, so a holster that feels too loose on the kitchen counter may feel perfect once it is carried at appendix.
The Sidecar ships with a mid-height sweat guard — found to be the optimal balance between keeping shirt tails clear during reholstering and avoiding the discomfort of a full-height guard jabbing into the abdomen.
Carry Positions
The Sidecar is optimized for appendix inside-the-waistband (AIWB) carry but is not limited to it. The included Sidecar Wing Attachment provides a second stabilization point that makes the holster viable at the 3, 4, or 5 o’clock positions. The Wing connects to the spine via the same pin-and-washer system and ships with its own tuckable clip, giving the holster two widely spaced anchor points on the belt for stability. Five adjustment holes on the Wing let the user fine-tune clip placement.
That said, the mold geometry, cant angles, and claw placement are all purpose-designed for appendix. At strong-side positions the Sidecar will work, but the Ironside OWB or the Raptor generally offer a faster, more ergonomic draw from those locations. Choose the Sidecar when appendix is the primary mode and you want the modularity of the spine; choose the Raptor when you need a single holster that works well across multiple IWB positions.
Attachment Ecosystem
Pistol Mag Carrier
The most popular attachment mirrors the classic sidecar-style appendix rig: a spare pistol magazine riding beside the holster. The carrier features five retention adjustment screws — more adjustability than the original Sidecar Appendix Rig design — with two primary screws controlling magazine tightness, an additional screw providing supplemental catch retention specifically for Glock magazines, and the remaining screws fine-tuning fit. The canted angle of the magazine carrier is intentional: it provides a natural index for the support hand during a reload while maintaining the concealment profile. The rigid Kydex-and-steel-rod spine prevents the magazine from tipping outward, a common failure mode in fully flexible holster designs. This attachment ties directly into the broader philosophy of carrying spare magazines as part of a complete carry loadout.
Tourniquet Carrier
Unlike the Kydex-based accessories, the tourniquet attachment is constructed from Biothane and elastic, creating an extremely low-profile and comfortable package. The primary design target is the CAT tourniquet, though it also retains the SOF Tourniquet and other items of similar diameter. A gripper tab allows the user to peel the elastic away for fast one-handed deployment — the design prioritizes speed of access over speed of reload, which is the correct trade-off for emergency medical gear. The carrier can even be worn standalone as an IWB tourniquet holder without the holster, and it ships assembled for right-handed shooters with a simple flip conversion for lefties. Staging a tourniquet this close to the body is a natural extension of EDC tourniquet carry methods and pairs with the training principles covered in CAT application drills.
Rifle Mag Carrier
For users who stage a rifle nearby — in a vehicle, a bag, or at home — carrying a rifle magazine on the body makes the transition from pistol to carbine faster. The rifle mag carrier uses four retention screws (two side, one top, one bottom) to accommodate the wide variance in magazine bodies, from polymer Lancer mags to steel STANAG to high-capacity options like the SureFire 60. Both magazine orientation (rounds forward or rearward) and clip placement are fully ambidextrous. The hinged spine allows even 40-round PMAGs to remain well concealed. This dovetails with rifle magazine selection covered in Magazine Reliability, Capacity, and Selection.
Subgun Mag Carrier
A more specialized option supporting SIG MPX, CZ Scorpion, MP5, KP-9, Stribog, and TP9 magazines. These carriers are fully ambidextrous and offer fine-grained retention adjustment. One practical note: Magpul Scorpion magazines have a slipperier surface than OEM magazines and may require tighter retention settings.
SD (Suppressor) Attachment
Originally launched as an April Fool’s joke, the suppressor carrier proved popular enough to enter regular production. It uses three retention screws and the standard spine interface to carry a suppressor in the appendix position — a niche but genuine use case for users who keep a suppressed pistol staged for home defense.
Wing Attachment
The default attachment included with every Sidecar. Beyond its role in stabilizing strong-side carry, the Wing can be experimentally paired with other attachments like the rifle mag or handcuff carrier for additional stability, though these configurations are not officially supported.
Design Philosophy and the Bigger Picture
The Sidecar embodies the principle of building a coherent loadout from EDC to full kit. A holster is not just a gun holder — it is the foundation layer of a carry system that scales from a bare pistol under a t-shirt to a pistol-plus-magazine-plus-tourniquet package under a flannel. The open-source spine system is a statement about how gear should work: standardized interfaces, user-configurable, and not dependent on a single manufacturer’s product roadmap.
The Sidecar is covered by a fully transferable Limited Lifetime Warranty — meaning the warranty follows the holster, not the original purchaser. If the product fails due to a manufacturing defect at any point during its service life, it will be repaired or replaced regardless of who currently owns it. This policy reflects confidence in the Kydex shell and spine hardware but does not cover normal wear, user modification of the shell itself, or damage from heat exposure (e.g., leaving the holster on a car dashboard in direct sunlight).
Setup and Configuration Tips
- Start with the holster body alone. Wear the bare Sidecar for a few days before adding attachments. This isolates comfort variables — ride height, clip position, cant — so that when an attachment is added, any new discomfort can be attributed to the attachment rather than a baseline holster fit issue.
- Adjust retention while wearing the holster. As noted above, belt and body compression change the feel dramatically. Aim for a setting where the pistol requires a deliberate upward tug but does not demand a death grip — the gun should not fall out during vigorous movement, but should release cleanly on a full-speed draw.
- Index the spine notches. When adding a pistol mag carrier, start with the magazine top flush with the top of the slide and adjust from there. Taller shooters or those with longer torsos often benefit from dropping the attachment one notch to reduce pressure against the belt line.
- Match clip material to use case. The acetal plastic clips are lighter, quieter against belt hardware, and gentler on leather belts. The spring-steel clips offer a more positive lock onto the belt and are better suited for rigorous movement or users who frequently don and doff the holster throughout the day.
- Test attachment swaps at home first. The push-pin system is fast, but fumbling with a friction washer and headless pin while standing in a parking lot is not ideal. Practice swapping attachments at a clean, well-lit workspace until the process is automatic.
Summary
The T.REX Sidecar is less a holster and more a modular carry chassis. Its spine system transforms a single purchase into a platform that adapts to the user’s evolving needs — from a minimalist appendix rig to a multi-tool carrier staging medical gear and spare ammunition. Combined with precision Kydex construction, optic-cut compatibility, and an open-source attachment interface, it represents the current standard for purpose-built appendix carry systems.