Improved end cap bolt

The spool holder by nxp200 is excellent, however, most of my spools inner diameter are too small to be able to mount on the holder without taking the end cover off. By doing this a few times I found the original en cap bolt a bit difficult to use, therefore, I designed a larger one with knurling that makes it a lot easier. I also included 2 versions, one with a shorter length that requires fewer turns to thread in.