OEM seat collar for a Cervelo R series bikes that take a 27.2 seat post. Includes 4mm hex bolt. This is the 4.5 Nm clamp with the bolt in the rear position and works for Cervelo R series bikes that take a 27.2 diameter seat post built prior to 2011.
Does not work on 2011 and newer R-series frame. Those require the 6 Nm clamp with the bolt in the front position and a small flat spot on the back