The standard Jelco grub screw is very small, so that is a problem if you want to cushion it with a nylon stub. My redesigned collar used a 6mm grub screw, so it was easy to find a bit of nylon of the right size (it actually came off the end of a UK number plate fixing bolt). I don't have much to suggest for a smaller stub, I'm afraid.
I'm sorry but there are no more collars available and I am not making another batch.