From August 1969, the oil channels in the crankcase were enlarged from 8 to 10mm and, at the same time, so were the oil cooler openings.
So to be able to fit the new 10mm oil cooler on an 8mm crankcase, VW devised this adapter kit.
Of course, you can also mount an old 8mm cooler on a 10mm crankcase the other way round. For this, the 3 washers, which lie between the cooler and the crankcase, must be used.