I'll get the post office to check it first. I ship 100 packages per month off eBay sales, most require package device due to thickness. Just can't remember offhand if it's 1/4" or 1/2" that kills the sorter. Had a few packages mangled, and a couple that ended up postage due at delivery.
Post is 3/16" x 1/2". I think I read the screw dimension somewhere above it in a thread I hit on google. Will see if I can find the data.
EDIT: Screw should be a #5 x 1" P-RH wood screw.