REF (Receiver Extension, carbine, FCD) is a 6 position, AR15/M4 standard carbine receiver extension (NOT A5 compatible). Made from extruded 7075 aluminum with rolled threads and dry film lubed interior, REF differs from most carbine receiver extensions thusly: Additional drain holes in the 2nd and 5th latch positions, in addition to the TDP spec carbine RE drain hole at the end of the RE. Laser engraved stock latch position indicators on both sides. Cerakoted. Forward Controls Design is not known for making modifications to TDP spec components just to be different. Different is just that, different isn't better. REF follows FCD's design philosophy, functi Mfg: Forward Controls Design