4BROS Sig Sauer P320 RaceCar Appendix Rig4BROS Sig Sauer P320 RaceCar Appendix Rig IWB Sidecar Holster for Sig P320 Pistols Built for comfort, concealment, and adaptability. The 4BROS Sig P320 RaceCar Appendix Rig is an IWB (Inside Waistband) appendix sidecar holster system designed specifically for Sig P320 pistols. Featuring adjustable sidecar spacing, a flexible injection molded adapter system, and customizable ride height and cant adjustments, the RaceCar Appendix Rig is engineered to