Photos provided by Andy Mason, UK, digitally processed and grouped by Jock Dempsey.
This style tool is usually designed to fit into a square recieving hole in the end of a long support arm or “horse” that would fit into hollow work. However, the one to the right is designed to fit in a standard holder.

This type tool can have a variety of geometric faces. The one to the left is elliptical, the one to the right is a flat round. Others may be hemispherical or ovoid (elliptical with different proportions on two axiis.