GARY TURNER GT X BILLET BMX HOLEY SEAT POST CLAMP 31.8mm (30mm w/ Shim)This Seat Clamp will fit most Aluminum frames with 31. 8mm size and 30mm frames with included shim. Does not fit 28. 6mm Gary Turner Chromoly frames see other listing for 28. 6mm size. GARY TURNER GT X BILLET BMX HOLEY SEAT POST CLAMP 31. 8mm (30mm w Shim) Billet BMX teamed up with Craig Turner to create an awesome collaboration featuring a custom designed Gary Tuner product line. These Billet Parts compliment all the hand made Gary Turner framesets