Bottom bracket bolts onto the rear cross-member.
Another view. This is fabricated from a bolt welded to a length of
steel strap, with a tubing sleeve brazed on to act as a spacer.
I had to file down part of the thread to fit through the holes in the
jack upright, which made it easier to drill a hole through for
a lock.
The bolt takes a spare wheel-nut (15mm fine thread, I think)
The top bracket bolts in with the spare-wheel carrier's hinge.
I put locks onto both bolts after losing a high-lift in Canberra (Australia),
when someone unscrewed the top bracket and used the jack as a lever to
remove the bottom bracket (and parts of the rear cross-member).
