Abstract: A clamp arm for attachment to the plunger of a clamping cylinder has a body with a central opening for receiving the plunger and a working arm portion extending outwardly from the opening. The body has a radial slot extending from the central opening and a bore in the body that extends transversely through the slot. One portion of the bore is threaded to receive a headed bolt to draw the sides of the slot together to lock the body on the plunger. The body is axially restrained on the plunger by means of a ring received in a counter bore above the transverse bore for the headed bolt. The ring is received in a circumferential groove in the plunger. Alternatively, the headed bolt that is used to draw the sides of the slot together engages a circumferential groove in the plunger.