Polar slider or push pin. this slider was originally made of black plastic. Ours is made of aluminum. Measures 9.5mm (.375”) in diameter X 42mm (1.625”) long. It is used to release the ﬂase clamp latch pin. Equal to Polar #241829. Only ﬁts the Polar 155 and 176 models. Comes with a plastic hole plug. Polar part #241827.