I made this descender in 1979, using a drawing from the 1967 Speleo Digest as a guide.
The Patten's hook is a homemade device. Mine is made from a 50 mm. length of 9.6 mm. (3/8 in.) type 316 stainless steel. The rod is bent to form an attachment eye at one end and a specially shaped 3D hook at the other. My Patten's hook is 260 mm. long, 65 mm. wide, 48 mm. thick, and weighs 279 g. Of course, other Patten's hooks could deviate substantially from these dimensions.
The Patten's hook works like an oversize carabiner wrap. I find that three wraps are about right for me. The wrap direction is not important for kernmantle ropes. On laid ropes, the wrap should be made in the same direction as the rope (i.e., right-hand for right-hand ropes) so that the device does not tend to unravel the rope. It is possible to add or delete wraps on rappel, but it is difficult to do so and I do not recommend attempting it.
The Patten's Hook is inexpensive, easily fabricated, and wears well. If properly made and used with the proper number of wraps, it is relatively safe. Aside from this, the Patten's hook is one of the worst rappelling devices I own. I find that on kernmantle ropes, I might spin a full 360° for each meter I descend. The situation is aggravated for laid ropes. This makes the device functionally unusable on free drops, so I never use it caving.