One manufacturer has changed the sizes of their JR G tubes to 12.1 and 10,4 OD, which is an increase of just over half a mil on both tubes. Be warned if you buy JR gents from ebay sources or other resellers as the old sizes are in the process of being exhausted and the new ones introduced. Any old spares that you have, such as the centre bands will of course not fit the new pens.
The new sizes are justified in that the centre band materials and the thread is reported to be a significant improvement on the old style.
