I am trying to understand where and what a trust ring is for in a hydraulic hammer? I understand that a trust ring allows rotation while having good axial strength. Why would the tool need to rotate? where is the trust ring? and how is it different from using a bearing?

A thrust ring is a type of bearing designed to resist thrust loads or loads along the axis of rotation. Tools rotate so that they contact the face being hammered across the entire face through the subsequent impacts.

It is usally located at the flange 2/3 or 3/4 the way up the shaft of the drill

See http://compare.ebay.com/like/300816...s&var=sbar

for an example.

Niel Leon
engineering.com