Hi Cath on the Forum IAP in the good ole USA there in the library is a fairly comprehensive listing of pen kits using a little engenuity and a caliper you could possibly reach conclusions. Over time you will find identical kits named several different names around the world depending on the suppliers.
I bought a hamper full including 150 Slimline kits from a mate who went out of turning pens and moved away, I have yet to do this exercise (no hurry since I mostly make Slimlines with Streamline centre bands from Timberbits . com). Mind you I have a problem determining when to use Red Green Copper etc kits but every now and again they come in handy.
Have fun along the way use new kits that have instructions while you solve the others.
Kind regards.
Peter.