Needle Size limits
If the listing for a particluler worm threader says it is only available with a small or small and medium size needle it means the hole in the handle will not accept a larger size needle.
I buy the stone handles already drilled for the needle. I do not as yet have the ability to drill stone. Maybe in the future I will but the equipment is very specialized and rather expensive.
I will ad some photos soon to illustrate the hole sizes.