Having decided to make an endpin clamp to hold the endpin firmly without causing damage to it, when shaping it to the required size, I used part of a massive 27inch X 1.25inch bolt that I dug up in the back yard several years ago and kept, knowing that one day it would be useful. The procedure was straight forward, being:
1. Cut a section 28mm long from the unthreaded section of the bolt, face the ends, drill a central hole 12.5mm in diameter and three equidistant holes, 1/8inch (3.175mm) in diameter, with the centres 4mm inside the outer circumference.
2. Cut a section 3.5mm thick off one end, face the cut ends, counter sink the centre to match the applicable shape or the endpin and then cut the opening to match the hole diameter and bevel the inner edges to match the depth and shape of the countersunk hole.
3. Cut another section 4.5mm thick off the same end, face the cut ends, drill the centre hole out to 12.5mm and cut the opening to match the hole diameter.
4. Thread the hole in the remaining section with a 9/16 inch UNF tap.
5. Make a stud by cutting an unthreaded 12.5mm diameter bolt to a minimum length of 30mm, cut a thread the full length, counter sink the end to match the shape of the endpin outer face and glue a rubber lining to it.
6. Counter sink the three holes in the outer face of the first section cut off, to match the counter sunk heads of the joining screws.
The three sections were then joined together using  3mm (approx.) machine thread screws and nuts, and painted, to finish the job.