Easy Safe Fitting. Sprung Jaws. Quick Lock-offSWL::- :- 250kg Tube diameter:- 38-51mm. The design of the clamp provides a higher degree of safety by allowing one person to hang heavy luminaries and scanners on any sized tube from 38.1mm to 51mm. The jaws are sprung to stay open leaving both hands free to lift and position the unit. The weight of the unit then becomes its own safety factor by automatically closing the clamp. This can then be locked off using the large Tee handle. The clamp base is slotted to hold captive either an M10 or M12 bolt head or nut.. doughty fixing-doughty trussing-doughty clamp