reenmachine
20+ Year Stangneter 

Not talking about an NPT threaded plug, but rather a press-in plug similar to a freeze plug. This press-in plug measures 3/8".red65 said:Gents -- it's actually 1/8" NPT (National Pipe Thread), which measures something like 3/8" across. You can run a 1/8"NPT tap into the existing dipstick tube hole on the side of the block and it'll take a thread (not a great one since it's not quite the right diameter for a 1/8"NPT thread, but good enough.) Go to Home Depot or the plumbing supply vendor of your choice and get a 1/8" NPT plug. You'll find that a 3/8" NPT plug is enormous and not what you want.![]()