Dumb question, I know...I've got two of these that I got with some other stuff. Haven't taken one out to measure but I guess these are for headsets, rather than a crank or something...eyeball looks like an inch but I'll get a ruler on it tonite. Getting ready to put 'em up for sale.

I've never seen one on the bay, and I've been looking!

Yes, it's a headset lock.

Here you go!