Mechanical pipe couplings for joining pipe elements in end to end relation have arcuate keys which engage circumferential grooves in the pipe elements and radially projecting stiffening ribs aligned with the keys. At the end of the keys on opposite sides are camming surfaces which are formed by a thinning of the key. The camming surfaces may be concave, convex, or angularly oriented surfaces and serve to guide the keys into grooves when the keys are not directly aligned with the grooves.