This specification describes connectors for tubes, pipes and poles, such as can be used in laser marking systems. In one aspect, an apparatus includes a body having a hole formed to receive a tube to connect an interior of the tube with an interior of the body, the tube having a circular groove formed in an exterior surface of the tube; and a clamp including a tab sized to fit within the circular groove of the tube; wherein the clamp is configured and arranged to attach to the body in a first state and in a second state, the first state being where the tube is held to the body axially by the tab and is freely rotatable, and the second state being where the tube is held in a fixed position relative to the body.