Standard Size 72mm piston. This is the normal piston you would exspect to find in the 300cc engine but there are very few engines with shorter pistons. Please Note the fitting instruction for this piston The Front of the JP piston is marked differently to the original BMW / Mahle/ Hepolite pistons which are marked with the word Front facing the Dynastart /Timing Chain We have been given instructions by the piston supplier after consultation with JP Pistons to install the piston with the word Front towards the Front of the car.