Ratchet mechanism ensures rapid, vibration and torsion resistant clamping. Clamping pressure: 1,000 - 1,200lbs (460- 550kg). Throat depth: 4-3/4" (120mm). Pivoting 1-1/2" contact plate with 3/8 - 16 threaded hole for adding accessories. Spring Stop for removing clamp arm. SPECIFICATION: 7" (178mm) Clamping pressure:1,000lbs (450kg) Rail size:7/8" x 7/16" (22 x 11mm) Weight:2.6lbs (1.2kg) 10" (254mm) Clamping pressure:1,000lbs (450kg) Rail size:7/8" x 7/16" (22 x 11mm) Weight:3.1lbs (1.4kg) 12-1/2" (318mm) Clamping pressure:1,200lbs (550kg) Rail size:1" x 15/32" (25 x 12mm) Weight:4lbs (1.8kg)