Is it really just a ring and a rope?
Yep it is pretty simple, but you'll want to make sure to use hardware that won't rust, and rope that is soft and flexible.
What's it for?
The toy's purpose is not to restrict blo od flow or maintain an erection, but to provide a sensation around the base of the erection when thrusting the hips. It also manages movement of the skin, testicles, and location of the erection.
What are the peices?
2 adjustable leg straps https://smile.amazon.com/gp/product/B0186ZHZLC/
1 adjustable waist strap
1 fixed waist strap
1 stainless clasp https://smile.amazon.com/gp/product/B078VRTZGV/
50mmx10mm steel ring https://smile.amazon.com/gp/product/B01K63W2KQ/
Will it fit?
The ring can be swapped out for any size ring, and can be found online by searching for Stainless Steel Round Ring and the desired inner diameter in mm. The straps are slightly stretchy, and three can be adjusted for length. The two straps that go between the legs, it is a simple overhand loop that can be removed and tightened at different lengths. The waist strap has an adjustable climbers knot youtube.com/watch?v=XkZnKLesw2A that should not be removed, only adjusted by sliding as needed. The knot should slide by gripping the rope in on the side it needs to move and pulling gently. Pulling on all three legs of the knot tightens it.
What size ring is good?
I found that a tight fit was not comfortable when worn with the straps, so I choose a size that did not put much pressure on my static erection. It actually decreases my girth because the lower lobe cannot stay as plump. When my kegels flex, it strains slightly against the ring. I recommend ordering a couple different sizes of ring to see what works for you, using a trial and error process. For example, I have a 45mm ring that does restrict blo od flow a bit, and is nice to play with without use of the straps. As I've been ligament stretching, I've found I needed to upgrade to a 55mm inner diameter ring https://www.ebay.com/str/cockahoops