I made this Peter Hamilton, Croydon Caving Club Rig 3 box in 2021.
My Rig 3 is 204 mm. wide, 38 mm. high, 38 mm. thick, and weighs 146 g. It is a single channel chest box consisting of a 6 in. length of 5/16 UNC stainless steel threaded rod, a turned Delrin roller with two needle bearings pressed into a central hole, and some nuts and washers.
I based this roller on the third of three "Cheap and efficient Chest Roller[s] for a ropewalker SRT rig" shown on the Croydon Caving Club’s web site.
In the interest of honest disclosure, I changed some of the parts, substituting 5/16" rod, nuts and washers for 10 mm, SCE57 for HK1012 drawn cup needle bearings, and turning my own Delrin roller rather than using a commercial dirt bike chain tensioner roller. I didn't try to scale the dimensions, so my rod is 204 mm. vs. 250 mm. on the original, and my aluminum tabs are larger than the original. I also omitted the keeper cord. Here is what the original looks like (image from the Croydon Caving Club’s web site):
The threaded rod on my roller is rigid enough, and I would expect the original to be so as well, so I won't comment on that. I’ll not comment on how well the rope might run on the original, but it runs well enough on my copy.
The idea of running needle bearings over threads should make any self-respecting machinist or engineer cringe. I know the idea was to make a cheap homemade chest roller, but I cannot recommend running bearings on threads.
The threaded rod is slipped behind the chest harness with the aluminum tabs placed in front to keep the harness from slipping off. The harness webbing runs directly on the threads, and this is another feature that I cannot recommend. The flat-top threads on the threaded rod that I used are not particularly sharp, but I don't like having these dig into my harness webbing. The ones on the M10 rod on the original look like they have sharp crests, which should be worse.
Finally, of for some reason one has bad technique and the rope slips off the roller, it will run on the threaded rod. Again, this would be undesirable.
Not having the original and because my copy differs in some respects, I won't rate the original, but I enthusiastically give my copy a Lemon Award:.