From 1980 to about 1984, VW ran only the small square pre-filter before the fuel pump. This filter (133-133-511) had a 7mm inlet nipple and a 12mm outlet nipple. The fuel tank on a 1980-85 Vanagon has a 7mm outlet nipple. The electric fuel pump on all Vanagons has a 12mm inlet nipple. The pre-filter also acted as a sort of adaptor.

Troy