 When detonated, the high explosive imparts momentum to the rods, thrusting them outward in an expanding circle.The pressure wave from the explosive needs to act evenly on the rods over their length, so some sort of tamper is used to shape the shock wave similar to an explosive lens.The rods are sufficiently soft (ductile) to allow the expansion without breaking the rods or the welded joints, and the detonation velocity is limited to under 1,150 m/s, allowing the rods to bend at these locations instead.