This plain aluminum block is a quick-and-dirty holder for round shanked boring tools.

I have been struggling with this holder for some time. The problem is that it fastens to the cross slide of the lathe with a single screw. The cutting force at the tip of a long boring tool puts a lot of torque on the axis of the screw, frequently rotating the block.
This block has two holes for tool installation because the first one was botched.

Here is my new holder for boring tools. I expect to have no further problems with rotation.