I bought this tilt and swivel some 20 years ago but never used it much. There are 6 set screws on the top of the moving block and I used to believe they are for holding some parts inside the moving block but the other day I found that the four screws indicated in the attached picture are just finger tight so I think they are just there to prevent chips from getting into the threaded holes which are there for mounting some accessories to the moving block. Any thoughts what those accessories might be ?