BULLBALLS ball-stretcher was the first and most popular silicone ball-stretcher, from Oxballs. It's now had a revamp with a more durable and usable design.
The  dimensions, thickness, diameter are as the original, but the shape is more refined, with a little more squeeze in the middle, a better rolled edge for comfort and better stretch. This thing just fits and feels right. Made of pure platinum cure medical grade silicone, it feels like skin and warms up to body temperature fast. It also doesn't irritate skin, so can be worn longer that stretchers made of other materials, like neoprene.
Made in USA - design copyright OXBALLS

Pure Platinum Cure Silicone

Lube safe: water-base, oil base, water/silicone hybrid, silicone lubes

Cleaning: detergent and hot water, dishwasher, or soak in bleach-water solution
Total Length: 2 inch/5cm

Total diameter: 1 7/8 inch/4.5cm

Usable Length: 2 inch/5cm

Inside Diameter: 1 inch/2.5cm