The ST1 model was their original model so its versatility keeps it as a #1 seller. Although designed to help with wider high cap magazines there is also a groove inside the mag well front and rear to align a 1911 style magazine. Years later and more innovations came along Adco expanded to a complete line as we offer now. If it is not and ADCO it's not a Super Thumb. The one that guaranteed not to break. ST1 21.5mm x 32.5mm a 1-1/4" x 13/16"Fits Most Double-Stack Magazines : Astra - A80 A90 Beretta - Cougar 8000 8040APX PX4 92 96 Bersa Ultra Compact Pro 9 40 45 TPR9C Browning - High Power CZ 75 97B Colt - 2000 and all 1911 equivalents FNP FNS - 9mm 509 TAC Glock 43 48 (also Mossberg MC1SC) HK - USP9 IMI - Baby Eagle IWI - Jericho Keltec - 9mm & 40 Star - 28 30 31 S&W - 59 Sigma M&P 9mm & 40 Sig - 226 228 229 250 320 365 SP2022 SCCY - 9mm Springfield -XDE XDS XDM XD40 Steyr - Mod. M Mod. 9 Taurus - PT92 111 917 G2C G3 Rock Island MS Ruger - SR9/P85/89/93/94/95/PC9 Walther - P99