The Rucker Machine Ruger Mark Series Red Dot Mounts attach to the top of the receiver on your Ruger Mark Series pistol, allowing you to mount a red dot optic.Silencer Shop has released a few branded versions of the Ruger Mk. IV, commonly called the Ruger SSH. Some of these pistols have a unique mounting hole pattern. In general, the standard version uses 3 mounting holes, and the SSH version uses 4, and the spacing of the holes is also different. On the SSH pistols, the mount uses two of the four holes, spaced 2.758" apart, leaving one hole exposed.