designed to work ONLY with KAK SIG tubes standard and super versionsTHESE RINGS WILL NOT WORK WITH OTHER MANUFACTURES TUBESused for adjusting the length of the sig brace for proper fit on the forearmthese rings are machined 6061 aluminumring spacer system mimics the last three notches on a carbine buffer tube (6 position tubes use .625 spacing)rings are slid on before the sig brace and trapped against the shoulderincluded spacer rings .625 and 1.250possible spacer adjustments .625 longer, 1.250 longer, and 1.875 longer (.625+1.25)long armed shooters will enjoy the longer length possible with this kit on their KAK sig tubesupgrade kit includes .625 spacer ring and 1.250 spacer ringbuffer tube and sig brace show for illustration and not includedTHIS BUFFER TUBE SYSTEM IS PATENT PENDING