A mechanical system that forms a cam follower or a rocker arm. The mechanical system includes a support element, a pin extending between two opposite ends along a first axis, and a roller mounted on the pin, movable in rotation relative to the pin around the first axis and adapted to roll on a cam. The support element further comprises an insert having holding members supporting the pin ends, provided with cut-outs having a shape complementary to the shape of the pin-ends, for assembling pin with insert by quarter-turn around the first axis. The pin ends each have a flat surface and an external surface. A first dimension of each pin end, measured perpendicularly to the flat surface, between the flat surface and the external surface of the pin end, is higher than half the outer diameter of the pin ends.