Ritchey WCS 1-Bolt Seatpost: 30.9, 400mm, 20mm Offset, BlatteThe Ritchey WCS 1 Bolt Seatpost features the patented SideBinder clamp desing that uses a single 5mm bolt for quick, secure adjustment. SideBinder clamp uses a single 5mm bolt to secure the saddle Wide saddle clamp reduces stress on lightweight saddle rails Works with all saddles with available clamp kits (ST3282, ST3283) Specifications: Defined Color: Black Offset (mm): 20 Diameter: 30. 9 Color: Blatte Material: Aluminum Clamp Style: Standard Rails