I am looking to see what other kits are compatible with the tube sizes. Anyone? Thickness of the blank is non-important and length could also be different to.
From the list in the library, the Tycoon is also one.
The woodcraft 5.6mm sketch pencil is a single tube design that uses the same diameter tube as the cap tube, but not sure if that's helpful based on your question.
The lower tube is 10mm and there are a boatload of kits that use that size.