The seams of the internal threads are eliminated by the reverse rotation while producing few chips，and uniform threads diameter is achieved even though the hole diameter is uneven.
The seams of the internal threads are eliminated by the reverse rotation while producing few chips，and uniform threads diameter is achieved even though the hole diameter is uneven.
正转时挤压出内螺纹，逆转时切去内径部的缝隙(有微量碎屑排出)，从而完成加工。下孔径尺寸即使零乱，也可以做出内径尺寸均一的螺纹。