Ritchey WCS 1-Bolt Seatpost: 31.6 400mm 20mm Offset BlatteRitchey WCS 1 Bolt Seatpost: 31. 6 400mm 20mm Offset Blatte. The 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) TECH SPECS Length 400 Color Blatte Diameter 31. 6 Material Aluminum