My guess is the description is a cut & paste job.
Whatever you do, don't pick 14mm—it sounds like whatever size you pick you can always remove the collet for the same effect (now how's it work without a collet
). Also, if I couldn't fit a 17mm hex into the bar (however redneck my research is), I don't think the interior diameter could possibly be 19mm.
I'd go with 17mm, but am not ordering these for the stock bar (it won't be long before someone chimes in with the precise answer, anyway).