check them out they seem to be making people happy im still running my 3 original prototypes and havent had a failure yet or even a roller wearing out they have really made my builds simple and all together a safer ride you can view them on ebay (motorized bicycle heavy duty chain tensioners usa) i have the rollers seperately also proto typing some motor mounts recently purchased a cnc machine trying to scrape time up to set up but day job is killing me !!