Ergotec Seat Post Atar (33.9 x 550 | Silver Polished)Features ergotec ATAR 550 is a patent aluminum seat post with 2 bolt clamping and 15 mm offset to the rear. This is suitable for saddles with 7 and 8 mm thick struts D. The ATAR seat post is now also available diameters of 33. 9 mm and 31. 6 mm. This eliminates the need for additional seat post bushings. Easy Adjustment of Components. You can adjust the pretension via the screw on end cap in order to regulate the progressive steel spring