This Dawson Precision Posi-Stop Baseplate is for the 120mm and 126mm mags only. Designed to fit Staccato P/XC/XL w/126mm mag or Staccato C2 w/120mm mag on Gen 2 Grips; with or without DP Tactical Advantage Magwell. Also works with STI Gen 1 Grips, with or without DP Gen 1 Tactical Advantage Magwell.