Nice vintage hit & miss engine piston and rod. Estate find of a large hit & miss collection so I do not know which engine it is correct for so consider pictures and measurements to determine if it is right for you. Connecting rod – ABY. Piston is 4 in diameter. Message from a collector (not confirmed by me but maybe helpful). The connecting rod fits both 1 3/4 HP and 2 1/4 HP Associated gas engines, in both the water cooled version and the air cooled version. If the piston has the letters ABW on it, then this combo is for a 1 3/4 HP engine. If the piston has the letters AKY, then the combo is for a 2 1/4 HP engine. I’m not certain, but I think the 1 3/4 HP would use a 3 3/4″ diameter piston and the 2 1/4 HP would use a 4″ diameter piston.