for Vespa ET4 50ccm 4T AC inner diameter: 16mm outer diameter: 26mm 2-hole Product description A porous manifold is an easy entrance part for false air which leads to deteriorated acceleration characteristics, a lower top speed and ?C in the worst case ?C can also cause damages to the engine. High time for a new manifold! But be careful: The scooter model is not the only decisive point here. Certain Modern Vespa models are equipped with different types of manifolds (e.g.: with one or two vacuum ports). So make sure to demount and check your manifold, before buying a new one. With some models so called shear bolts were used. We recommend exchanging them for regular hexagon bolts when mounting the manifold. Community User “tcpip1″ (on part no R100520040): fits perfect, good, original and low priced” OEM numbers (for comparisons): 969405 (PIAGGIO)