For 50mm Bars. Strong Bar Coupling. Rigid Assembly. Dual Bolt fixingSWL: :- :- 750 kg Tube Diameters: :- 48 to 51mm Width: :- :- 50mm Tube Centres: :- 110mm Weight: :- :- 1.33 kg. The Doughty Parallel Coupler provides a firm fixing between two parallel bars. The bars can then be attached to other structures with the bolt fixings- or be suspended as part of a flying rig.. Doughty parallel-doughty coupler-trussing coupler