Mount your radar tail light or bike tail light (both sold separately) to a D-shaped, aero or round seat post with these quarter-turn mounts. Round model Includes mount and 2 fitting shims. Compatible with round seat posts from 27.0 mm to 31.6 mm in diameter. Universal model fits D-shaped, aero or round seat post. Includes mount, 3 fitting shims and 2 O-rings. Compatible with round seat posts from 25.4 mm to 35.0 mm in diameter; Aero and D-shaped seat post compatibility varies by bike model. About GarminGarmin produces activity trackers and sports watches, for activities such as running, watersports, golf, cycling and swimming. From introducing their first wearable GPS unit in 2003, Garmin is a leader in GPS for units for sport and fitness tracking.