O-rings Umnumzaan for the thumb pins of your Umnumzaan made of shock absorbing polyurethane The O-rings dampen the impact of the pins against the handle.Thus, the knife opens almost silently and also gives a very rich feeling when the lock engages. To change the rings, simply pull the old O-rings off the stoppins and carefully slide the new ones into the designated groove. Scope of delivery: 1 pair