I've never locked a helmet and never lost one. I don't like hanging them upside down....did it once years ago, it rained a little and I ended up with a helmet full of water....no real big deal, unless you have a headset in it. Now that I have the Ultra the tour pack will be reserved mostly for helmets, but if I'm stopping at places around town I usually just set it in the passenger seat, the drivers backrest holds it snuggly in place.

 

7.8 MM Shank that goes thru the hole in the handgrip area. 6MM Sthreads on the end. The entire shank and threaed part is said to be 1-5/8" long according to Kuryokin (sp?). Hope this helps. It will work. Like I said when I get it done I will take pics and post em.