Mark,
JR Gents top bushes are approx 13.35, barrel is 12.25 (and 11.61). JR Gents II top bushes 14.35, barrel 12.15 and 12.91. The larger bushing is for the nib coupling. I never realised that the JR Gents II had different dim bushes for the ends of the barrel. So I measured the OD dims of the JR Gents bushes that I bought from TB many moons ago, and sure enough, and I never realised (I always turn the barrel proud of the bushes anyway as the pressings that form the metal rings around the plastic inserts are dimensionally crap), they are slightly different,
The jr Gents obviously take a 15/32 and a 25/64 tube, but the bushes that I have and never used (bought in error) show that the Jr Gents II uses slightly bigger tubes, ID of the top Jr Gents tubs 10.85, ID on the JR Gents II 11.65. ID on the JR Gents barrel tube 9.04, ID on the JR gents II barrel tube 9.55.
So, measure the OD of the metal ring that encircles the nib coupling on a TB JR Gents kit and the dim is 12.22, the ring on the postable end is 11.77 which supports the theory that the bushes are supposed to be different dims.
Every days a learning day, the dims for the Gents barrell are different, the TB instructions don't indicate that and I wonder if there are batches out there that are the same? Could anyone else out there with TB or other source JR Gents bushes measure the OD of the barrel bushes and post the results?