"For high grade 316 stainless 18x1.5mm threaded weld-on 02 sensor bungs I recommend contacting JGM Automotive Tools (714-895-7001) and ordering p/n TR-18 (cost $12.60 each). They also sell 316 stainless plugs with copper washers to plug the bungs if you ever want to move the 02 sensors to the exhaust manifolds like I have. Another quick and inexpensive source for bungs would be to obtain an 18x1.5mm stainless nut from the hardware section at a local marine store or from Totally Stainless (800-767-4781)."