Abstract: In a rotary coupling, such as the coupling between a piston pin and the holes for the same bored in the bosses of a piston for an internal combustion engine, a device for improving the lubrication, comprising a number of turns of capillary circumferential groove hollowed in one of the coupling surfaces, said groove having preferably a depth ranging from 5 to 20 .mu.m, a pitch ranging from 0.25 to 1 mm and an eccentricity not exceeding 2 .mu.m.

Abstract: A piston for internal combustion engines, of the type having a crown portion and a cylindrical skirt portion in the latter of which are formed thickened portions called bosses having holes for receiving the ends of a gudgeon pin by which the piston is attached to a connecting rod, in which provision is made for avoiding thermal stresses and possible consequent damage due to the variations in wall thickness in the region of the bosses by forming therein two interior chambers each communicating with the interior of the piston and with the respective hole for receiving an end of the gudgeon pin via ducts through which the engine lubricating oil flows as a coolant when the engine is running.