hollow pin

基本解释

Its upper end is drill pipe box or union, the nether end is casing pin. It is a crossover with hollow inside .
它是个上端为钻杆母扣或者由壬，下端为套管公扣，内空心的转换接头。
A coil compression spring is captured to the pin in the hollow core of a segment and urges the adjacent components together.
卷曲的压缩弹簧被固定在段的空芯内的销上，并促使相邻的部件互相靠近。
ip.com
The utility model comprises a nut cutting sleeve (1), a hollow guide tube (2), a metal ferrule (3), a pin (4) and a handgrip (5).
本实用新型由螺母卡套（1），空心导管（2），金属箍（3），销钉（4），手柄（5）组成。
ip.com

The government may simply insist that 3D printer manufacturers install software that prevents printing of a hollow cylinder of a certain size, a firing pin, or a certain type of spring.
FORBES: Five Reasons Gunmakers Have Nothing To Fear From 3D Printed Guns