I was looking for an antenna bracket that would fix to a camera tripod, and allow vertical antennas on 2m/70cm, and a pair of HF whips horizontally. No such thing appeared to exist, so I designed one. The easiest way appeared to be to use Schaeffer‘s Front Panel Designer. It wasn't really designed for the purpose, but with a couple of compromises, it worked just fine. In case anyone wants it, the design file is available. Please note that the SO239 flange is metric, and assumes an M3 bolt. The holes should be in the same place, and so easy enough to change if you want an Imperial one.
The SO239 in this case is RG58 crimped, and then heatshrink sleeved. The cable is ~15cm to an SMA plug for portability. The smaller hole is 1/4 UNC to attach to the tripod. The larger hole is 3/8 UNF to attach to most small antenna studs.
Attaching the V/U vertical is obvious. Radials or ground wires can be bolted to it using the UNF hole.
The only thing to watch out for is that Aluminium oxidises to a low conductivity, so you may want (passivated) star washers etc. to keep the contacts working, and be aware of the potential for rectification across the electrolytic junctions. It’s really not for leaving out in the rain.
And finally we have the horizontal HF dipole mount. (That’s still the 70cm whip on the socket, rather than something more suitable.) By flipping the bracket around, we get the 3/8 hole exposed in the opposite direction to the SO239. So the centre connector runs the directly attached antenna and the braid runs the stud mounted antenna. The addition of a current balun or similar convinces it to form a balanced dipole, conveniently insulated from the tripod by the rubber on the quick release plate.