Maybe a dumb question, but now that I'm making fountain pens it occurs to me to design a combined section/housing as a single piece instead of making a custom section to house a purchased housing. The housing is just a tube with some threads, seems simple enough. A combined unit just needs to have an appropriately sized hole to friction fit the nib/feed assembly (how hard can that be?), and a threaded tenon to attach to the pen. Am I missing something obvious?