One of our favourite sites is American-Gymnast.com
They have a “pommel tips” page with equipment recommendations, notes for coaches and video clips.
Here’s an interesting one:
Elbow circles, on a mushroom with a bucket, are a useful way to facilitate the straight body position. This drill allows the gymnast to build muscle memory in the right position.
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American Gymnast | Training Tips | Technique | Pommel Horse
(Of course you are going to crash once in a while. We would put the mushroom right on the floor to reduce the height of the drop.
The Altadore Gymnastics pommel bucket, by comparison, is excellent, the bucket held by a twisting spotting belt, suspended by link chain. It is easy and quick to change the length of that chain using a caribiner.)
Gymnastics Coaching.com 