Abstract: A novel surgical instrument suitable for insertion and assembly of multi-ring compression devices for circular anastomosis of tubular tissue sections including a body having means to support and align the rings, means for clamping the rings around the free ends of the tissue sections, means for coring away excess clamped tissue and the centers of the rings, separate means for releasing the clamped rings from the instrument and dwell means to delay releasing the rings until after the coring operation is complete. The dwell means consists of an external cap containing separate and coaxial elements for the coring means and the releasing means which are provided with a series of recesses and a plurality of shifter keys to separate the operation of coring from the separate operation of releasing the assembled multi-ring compression device from the instrument.