A good copy of the discontinued b-square dovetail mount - Sun Optics Ruger MK Handgun Non Drilled Universal Mount

I haven't done a side-to-side comparison of the Sun Optics mount with the old B-Square mount, but it looks just like what I remember of the B-Square mount. For a slip-on mount, this provides a very, very solid mount, without the need to drill and tap the pistol. It's the perfect solution if you have an old MKI or MKII model that is not drilled and tapped, and you want or need to use optical sights.