This specialized sl pave carbon seatpos with 21 mm set back is lightweight and comfortable vibration damping post allows you to fine tune your saddle position with a single bolt adjustable head and 21 mm set back the post is made from fact 3k sl high strength carbon which is a blend of durability stiffness and comfort specialized have included hardware for 7x7mm and 7x9mm rails the integrated vibration damping zertz viscoelastic polymer insert helps make this post one of the most comfortabl