The output shaft spacers help keep the clearance between the shift gears, otherwise known as the float end, to a minimum to help the gears engage clean. Spacers in pre EFL PX engines only have 1 stability tab and later (after DFL) shims have 4. The later EFL version can be retrofitted to earlier PX engines. The PX EFL output shaft requires the use of at least 2 spacers and also 2 snap rings, one of each being at the ends of the gear cluster. The more stable PX EFL gearbox parts are usually used in tuned PX engines. Due to the higher horsepower levels produced by more performance orientated engines the correct gear clearances becomes essential. To allow for a more precise float shaft end distance, to the hundredths of a millimetre, to be achievable SIP have produced the thinnest grades of gearbox spacer to complement the existing range of sizes manufactured by PIAGGIO. Your change box will thank you in the end for a quieter (and longer) life. Tip: The float distance end of the output shaft assembly should be between 0.15 and 0.4mm when it is just pushed together. If you are experiencing it during a major service it should grow to be under 0.5mm otherwise you will require new (thicker) spacers… SIP-TIP: The feeler gauge for measuring the axial play of your output shaft makes this job much easier. It is available at our shop, Art. No.60824000. Don't forget to order a new cross, barrel selector and fresh gearcase oil to get the job done properly.