When clamping a workpiece to the mill table you usually have to clock an edge to make sure that the workpiece runs true.
This morning I set about making a couple of items which clamp inside the t-slots and can be used as a reference edge to locate work. (T-slots are normally cut very precisely w.r.t. the travel of the machine.)
I just happed to have plenty of 6mm gauge plate (or ground flat stock) so I cut a couple of pieces and squared them up on the mill.
The screws were M6 x 12mm hex head set screws. I had one of my assorted boxes of nuts and bolts spread out and found dozens of M6 x 10mm but when I measured the heads they were 10.4mm a/f! I haven't a clue why they'd have a non-standard hex but as I don't have a 10.5 a/f spanner I continued my search through another box until I found four with the correct heads for a 10mm a/f spanner.
The head ends of the threads had to be relieved so that the head would close up to the bar and the heads were slightly domed so they only contact in the centre.
There are two sets of holes in case I need to set them at different heights in the t-slots.
I thought I'd finish them off with the chemical blacking kit and, much to my amazement, the remaining zinc plating on the screws also turned black.
