A device for cold working pipe elements has two or more cams, each having a gear which meshes with a pinion to turn all of the cams. Each cam has a cam surface with a region of increasing radius and may have a region of constant radius extending around a cam body. Each cam also has a traction surface extending around a cam body. A region of reduced radius in each cam surface is aligned with a gap in the traction surface of each cam. The regions of reduced radius and gaps provide clearance for insertion and removal of the pipe element between the cams to form a circumferential groove when the cams are rotated.