Steve P is correct, the front sight off a T512 Mk. II for example, would work well, if you can find a used one. However, Ruger no longer stocks them and considers them obsolete. They are now replaced by a patridge front sight on the Mk. III which is not undercut, like those on the Mk. I and II were. They have a narrower base, and fit the single six perfectly. I recently bought 2 for a pair of 4 5/8" stainless Single Sixes, and really like them. The cost is about $9.50. They can be ordered through Ruger's parts department in Prescott. The height is just a few thousandths shorter than a Single- Six ramp, about .340" if I recall correctly.