Since '93 Smith&Wesson has been drilling most K, L, N frames for mounts. The holes are hidden under the rear sight, but you can open the cylinder and look at the bottom of the top strap to see if your's is drilled. Prior to '93 models can be drilled and tapped by a gunsmith. There are a couple of mounts that do not require the mount holes. These either pinch the top strap or use a barrel clamp or band. They are bulky and unstable. I tried them, then had my 686 no dash drilled and tapped. I am much more pleased with the results. This is the base I used made by Weigand.