All 356/912 engines have a steel plug in the bottom of the engine case to drain the oil. This plug has metric tapered threads.

Tip: It is a common misconception that 356/912 drain plugs used copper crush washers for sealing. In fact, the 356/912 engine never used a washer. Using a crush washer can result in damaging/distorting the drain hole on your engine case causing leakage.