This reducing coupling is 3/4" barbed insert x 1/2" barbed insert for PE flexible pipe. The 1/2" barbed insert end measures 0.406" inside diameter and 0.665" outside diameter barbs and the 3/4" barbed insert end measures 0.562" inside diameter and .865" outside diameter barbs. Polyethylene pipe should be clamped with one clamp directly over the barbs.