This aluminum adapter has 12x1.5mm male threads on one end and an 8AN male (3/4-16 thread) on the other. This adapter fits the outlet side of the popular Bosch 044 Fuel Pump (Part No. FS FP044). The metric end is hollow, without a sealing surface. You must use a 12mm Aluminum Crush Washer (Part No. 3278-M12, sold separately) with this fitting.