The collets are brass bushes drilled 10mm for the riser posts. There are M4 x 12mm grub screws let into the woodwork that go into tapped holes in the side of the bushes, to nip the riser posts.
I put the bushes in place, then drill and tap the wood and the bush in one go. The bushes don't need to be glued in as they can't come out once the grub screws are in place.
The riser posts are 10mm. I drill the cheek piece underneath to take the top of the post, recessed about 15mm, making one post a tight fit and the other one with about 0.2mm of clearance, then a spot of Araldite on the end of the posts. Just don't get the epoxy down between the post and the bush.