Spring Pins go by many different names, including spring tension pins, Sellock pins, roll pins and slotted spring pins.
Spring pins are a self-locking fastener that use tension to hold two or more components together. They are essentially a small hollow steel tube without a head but with chamfered or rounded ends. The pin is slightly larger than the hole that it is being introduced to, so that once inserted into place the outside walls of the sprung steel pin exert pressure and hence grip the hole, holding the pin and the components in position.
To insert a spring pin, cover it in a light lubricant and grip the pin with a pair of long-nose pliers. Offer the chamfered end of the pin to the mouth of the hole and gently tap the pin into position with a small hammer.
Spring pins are available in both metric and imperial sizes.