Transmission manufactures have been required of performance improvement and miniaturization for the AT (automatic transmission) or CVT (continuously variable transmission) unit from car manufactures. Current unit is composed of Aluminum piston, O-ring (or D-ring) and drift ball. We changed design from O-ring to lip type seal and aluminum piston to high strength steel plate piston in order to miniaturize. On the other hand, we changed drift ball to canceler in order to make faster response. At this time, we selected new lip design and developed high tensile strength ACM to keep as same oil pressure resistance and durability as current O-ring. In addition, we could have lower friction with new design of lip shape.