21mm, Designed to fit a 21mm sway bar. Whiteline's sway bar mount bushings not only boasts the latest in bushing material technology but feature a knurled ID specifically designed to retain grease. Backed up by a Limited Lifetime Warranty. Whiteline bushings are made from the latest highest quality synthetic elastomer and designed to synchronize your suspension system for optimal safety, handling, performance, ride quality, longevity and reduced maintenance. They are the most positive link between your vehicles body, springs, struts, arms, bars and shocks., Limited Lifetime Warranty