US Patent 7789434 Coupling with concave bearing surface

A concave bearing surface for use with lugs of pipe coupling segments and a method of joining pipe ends. The concave bearing surface is positioned on the lug and surrounds an aperture which receives a fastener attaching the coupling segments together end to end surrounding pipe ends to be joined. Either the nut or the head of the fastener that engages the concave surface may be rotated to tighten the fastener. Engagement between the concave surface and the rotating member reduces the torque required to tighten the fastener and effect a stiff, fluid tight joint.