Caliber 9 mm Capacity 15 High Cap Flush Fit Fits P.228 and older P.229 pistols with flat-sided narrow magazine Not for use in P.229 E2 pistols with wider tapered P229-1 magazine Increased 15-round capacity in a flush-fit design. Features US Patent# 5,386,657 which provides two additional rounds without increasing magazine dimensions Carbon Steel Tube, heat-treated for strength Higher tensile music wire spring Polymer follower Removable steel butt-plate