DIN 1481 heavy-duty spring pin
A spring pin is a hollow cylinder which has a longitudinal slit from
one end to the other. It has a diameter greater than the nominal diameter
of the circular slot where it is to be fitted. When the spring pin is
introduced in the hole it is compressed and retained due to the elastic
force which it exerts on the walls of the slot. The longitudinal slit narrows
but stays slightly open.