This Bessy clamp is designed to interlock with the rail of a bar clamp, letting you apply force to the edge of a work piece while making use of the clamps you already have. A thumbscrew lets you securely attach the single-spindle clamp to a rail up to 1/2" thick. Wing-nut securely attaches the 5-1 to clamp. 11.5 x 29.2 x 3.2 Centimetres 3 clamps available: $12 each, or all 3 for $30 Note the seller is in Metchosin; still available if ad posted