You may be right, the thread pitch and diameter are so close that it’s difficult to be certain, but the thread angles are sufficiently far apart that there should be jamming on a longer thread. A 6BA nut fits perfectly on an existing indicator point, and a 6BA machine screw goes to the bottom of the hole in the indicator (about 12mm) without any sign of jamming …. so I suspect that it really is a 6BA thread. The thread length on a “point” is quite short so a 4-48 would probably fit, but I’d prefer to get the right one to avoid any risk of jamming or wobble.

peak4: my Mercer 1/10th and Baty 5/10 DTIs have the same thread – fairly certain it’s 6BA now.

SB5: a DTI elephant’s foot is just an accurately ground flat disk with an appropriate thread. I need one 8-10mm diameter and 6BA, so thanks for the kind offer but the size and thread are both wrong.

PK6: yes, you’ve made me feel guilty. I hadn’t fancied having to cut a 6BA thread on an 8mm piece of bar and hadn’t  thought of using studding into a tapped disc. I think that, for repeatability, I’d want the disc to have a shoulder that could seat on the face of the DTI “shaft”. I guess I’d turn a tapped cylinder to simulate the DTI in the lathe chuck, screw the foot onto it so the shoulder seats, and then turn the base of the foot – I’d prefer to grind the foot, but I can’t think how to do that … Maybe it’s simpler to “adjust” a 4-48 thread!