From the context crumbs that Gyptis has strewn over the course of this thread, I understand the following:
1 This is a size reduction equipment which has grinding elements that will wear over time - a hammer mill.
2 Hammers should be rotated when the leading cutting edge is rounded/worn and the machine is not operating efficiently any more.
3 Depending on the application, hammers can be either 2-way or 4-way reversible, indicating the number of rotations possible before replacing. This seems to be 2-way reversible hammers (one hole for threading rod/pin through?)
4 Once the hammer has been rotated/flipped by 180 degrees, place it back in the holder.
Das hätte ich natürlich auch gleich so ausführlich erklären können, doch an dem Tag hatte ich leider wenig Zeit.)
You found time to post six answers that day.