Xtra Thick Is RightDoc Johnson's metal cock ring xtra thick is just what the name suggests. It is a 3/4" thick ring of aluminum for use as a cock ring. The aluminum construction means it is very rigid. It is designed to be worn on the penis behind the testicles or on just the testicles to provide a stronger, longer lasting erection. It comes in 2", 1-3/4", and 1-1/2" diameters. The smaller the diameter the more effort it takes to wear and the more effective it usually is. All that and it looks pretty cool too.
Another option is to use the smaller diameter rings just around the testicles for a slightly different effect. The 1-3/4" ring I have took some effort to get over the shaft, and I considered just using it around the testicles, but the additional effort was worth it as the effect on my erection was noticeable and pronounced.