GrovTec US Browning BL-22/Astra 357 Hammer Extensions Black. Specifications for GrovTec US Henry Big Boy Hammer Extensions: Manufacturer: GrovTec US Color: Black Fabric/Material: Steel Condition: New Package Contents: GrovTec US Henry Big Boy Hammer Extensions What firearm models does the manufacturer say GrovTec US Henry Big Boy Hammer Extensions is compatible with? The manufacturer says that GrovTec US Henry Big Boy Hammer Extensions is compatible with Marlin Model 36 Marlin Model 336 Marlin Model 444S Marlin Model 62 Marlin Model 57 Marlin Model 57M Marlin Model 444 Smith & Wesson Model 29 N-Frame Revolver Thompson/Center Contender Marlin Glenfield Model 30A Marlin Model 1984C Marlin Model 1895S Winchester Model 1894 Marlin Model 375 Marlin Model Golden 39A Henry Single Shot Winchester Model 1894 Angle Eject Winchester Model 1894 Big Bore Ithaca X-Caliber Henry Big BoyGrovTec US GTHM71: Browning BL-22/Astra 357 Hammer Extensions Black