IRWIN 225104 100 Series 4-Inch C-Clamp
The IRWIN 4" C-Clamp 100 Series has many improvements over the competitions.  The handle is bigger which makes it 25% easier to apply torque.  This feature will reduce hand fatigue and make it easier to apply force.  The double threaded screw allows you to create 50% more pressure than the nearest competitor.  This will reduce hand fatigue and make it easier to apply force.  The double threaded screw will give you 50% less screw deflection which will save you time by reducing drift.