About 15/16" or 23.5mm, probably 1" nominal
By grommet, I assume that you mean the bearing.
Joe, as one of our inquiring minds, have you given any thought to what would be the effect of making that length shorter, say, 5/16".
From time to time I brush against mine on the way to unlatch the hangar door on the far side.
Shorter would make the contacts less likely with less stress on the tube.
How about this? You could skewer a pig on that thing?-
Well, according to http://www.hochwarth.com/misc/AviationCalculator.html I was pulling about 0.19491 MACH on my way to breakfast on Saturday in my RV-12. Clearly those thousands of raised pulled rivets reduced my speed by at least 0.00805 MACH. Takes a big man to admit that his pitot tube might be a little short....will be sure to keep the cover on it when I'm on the ground now on, as I wouldn't want to embarrass myself in front of those other RVs with longer tubes...