The radiator was not equipped with a drain plug. I can't find replacement drain plugs by searching online by brand name. I can't find any information on the thread size/drain plug specs either. My radio's OEM drain plug will not fit. I will try to contact skunk2 support directly for information on how to get a replacement drain plug or look up the drain plug manufacturer's specifications so I can find a replacement myself. But without a drain plug, this item is essentially junk aluminum, and I don't want to stick random screws in it and risk stripping the drain plug threads on a $200 radiator.