SIGEYI "SACS" Single Arm Cage System - GRX

This is Sigeyi's SACS — Single Arm Cage System. A replacement rear-derailleur cage machined from 7075-T6 aluminum, designed to drop rotational mass and sharpen shift precision on supported Shimano and SRAM derailleurs. The single-arm geometry runs a single pulley-carrier side plate (instead of the stock cage's two-plate sandwich) and re-routes the chain with the factory guide/tension pulleys.