Reference is made to Craig’s enquiry re the spring collets. I have a set (holder and collets) with similar dimensions to Craig’s which were purchased from Clarke many years ago. I did try to purchase a few imperial sized collets and did a lot of searching before a colleague on the other side of the pond identified the type as Q24-16/MS3. Unable to source from the UK so will probably have to solicit some help from abroad. The part number I have on file for the set is 7610323. Hope this is of some help.