A rotary mower has a cutting plate to which freely pivotal blades are attached by retaining pins. Instead of riveting the pins directly to a leaf spring which holds the pins in place, a keyhole slot is provided in each leaf spring and a narrow waist of the retaining pin fits into rectilinear portion of the keyhole slot and is held in position there by a holding plate riveted to the leaf spring. This allows case hardening of the entire retaining pin and prevents nonuniform stresses in the latter from causing breakage.