Whitworth? I haven't dealt with Whitworth standard fasteners since the MG TD :) Camera tripod threads are typically 1/4-20. There is a European 3/8-16 standard also, but I haven't seen it anywhere but view cameras and tripod head-to-legs.
That camera trivia aside, gadgets have been made to entice photographers since Matthew Brady was a boy. I have a simplified version that is all metal and weighs 2 ounces. I've used it maybe twice in 30 years.
I concur that these belt clips leave the camera vulnerable to brush and all the other trail hazards, flopping around right where you can bang your arm into it. IMHO, most of these gizmos were made with sports photographers in mind.
Think Tank makes some very high quality holster style cases that can be mounted on a hip belt, but they add a pound and yet more bulk to your waist belt. Most of the other players like LowePro and Domke have their version
The only rigs I've seen that suit backpacking are chest mounted harnesses and cases. I find them all annoying, but if you must have your camera immediately available, that's what works best. A case with a lid that tips out gives the best access and still protects the camera. The smaller Lowepro. TLZ series aren't too bad and have enough d-rings to allow hanging them on your backpack shoulder straps.
You can sit down with a small pile of tri-slides, snap hooks and webbing to cobble up some links in a few minutes. Having something with side release buckles helps, because you need to release at least one side to get your pack off
The other chest option is a neck strap with some sort of elastic to your belt or other way to keep it from bouncing. In the old days with a Canon F1 and lens weighing 42oz, it was like having a bully poking you in the solar plexus if the camera bounced as you walked. Not good.
I prefer an assistant for hauling the gear--- let's me concentrate on The Work :)