Grams Mag Follower Kit - STI

11 Coil ''Follower Kit'' includes a ''Grams Format'' follower and 11 coil spring. It will fit SPS, STI or SV magazines that measure up to 145mm in length (with base pad attached). 13 Coil ''Follower Kit'' includes a ''Grams Format'' follower and 13 coil spring. It will fit SPS, STI or SV magazines that measure longer than 145mm and up to 171mm in length. Will work with .38/9, .40, .45 calibers. 9mm kits are designed for the 9mm x 19 caliber, when a spacer plate is used inside the magazine tube.