O-ring style manifold for 1955 - 1965 Harley-Davidson big twins with stock 5.330" cylinders. Manifolds for 1955-1965 panhead engines with o-ring style cylinder heads are available in 1 7/8 bore only. 1936-1954 knuckle and pan cylinder heads with plumber style intake mounting nipples must be converted to accept a 1955 to 1965 o-ring manifold S&S Part #: 16-1100