The Brompton bottom bracket hinge pin is held in place by two UNF Allen head bolts. It so happens that the nut of an M2 bolt fits perfectly in the Allen head, so I fashioned a couple of clips from sheet metal, with an M2 nut and bolt in just the right position to slot the nut into the Allen head. The nut is positioned well inside the Allen head by use of a tiny spacer under the nut. Should the machine screw try to unscrew, it will be held against a tightening nut. I'm hoping this will eliminate the need for the use of thread-lock on the machine screws, which is how Bromptons are built. The sheet metal, by the way, is the screening out of a dead laptop power brick. I was thinking of holding the locking plate in place by drilling and tapping a hole in the triangle for a small bolt, but I would rather not compromise what is a high stress part of the frame.
