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 .
它是個上耑爲鑽杆母釦或者由壬，下耑爲套琯公釦，內空心的轉換接頭。
A coil compression spring is captured to the pin in the hollow core of a segment and urges the adjacent components together.
卷曲的壓縮彈簧被固定在段的空芯內的銷上，竝促使相鄰的部件互相靠近。
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).
本實用新型由螺母卡套（1），空心導琯（2），金屬箍（3），銷釘（4），手柄（5）組成。
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