You can't get a great action job with out cleaning up every bit of roughness inside the Single Action Army's frame. You'll be amazed at how much you can reduce the single action's cocking effort and lighten perceived trigger pull without ever touching the critical trigger/hammer notches. Well worth the effort on first and second generation Colts, especially important on 3rd generation and clones with cast or roughly forged frames. The MF-414 stone fits nicely in the hand slot and cuts quickly to get rid of casting roughness. Follow with the HF-823 to make a slick, polished path for the hand. Use the MF-14 to round the nose of the hammer notch. Thanks to Eddie Janis of Pe Mfg: Brownells SPECS: Kit contains three stones in padded plastic box: MF-414, MF-14 and HF-823. Dimensions are approximate and may vary. MF-414 - medium India, 5/16" (7.9mm) wide x 3/16" (4.8mm) thick, tapers to 1/16" (1.6mm) thick x 4" (10cm) long; MF-14 - medium India " (6.3mm) square x 4" long.