I took my wall street lower end apart and have posted pictures. the nib measures .295 at the end that would go into a tube. That does not correspond to any of the standard tubes we use. IE. 8mm is .286 and 3/8th is .342. the nib is pressed into the brass piece, which is tapered. there by pinching the tapered lower barrel. the upper threaded piece measures .444-.446 o/d and .305 i/d where it goes into the lower tapered tube, besides pressed in it had a glue residue as well. The lower tapered piece has a wall thickness of .012
I have added the finial/ clip picture this morning.