I bought 2 of these for my 1985 Yamaha Tri-Z. The lower one fit perfect without any kind of modification. The upper was a bit more challenging. There is a stock stud on the bike, and the chain roller in factory form does not fit over it. So, I popped the bearings and center guide out of the roller and then pressed the stock, white, plastic sleeve into the roller using a bench vice and a socket. Problem solved. Then I just had to loosen the gas tank to get enough room to pop the roller back over the stock stud and used a couple small washers to ensure the black roller material didn't rub against the mounting point which would cause it not to spin. Worked great.
Bearings blew out of old roller so I purchased this as a replacement. Hard plastic rather than rubber. Was a surprise to me. But this material should hold up better to the harshness and roughness of the elements of riding. A little pricy for a piece of plastic with bearings though. Still would recommend.
I replaced the roller on my quad along with a new chain & new sprockets. It has worked fine for about 2 months now. It seems to be well built for the price. I would have liked a few more color options. I ride a green & black Kawasaki, so green would have been nice.