I used a 1/2" NPT brass plug with a little tef. tape. Works perfect, being NPT the threads are a little loose in the beginning but 2/3 of the way in it was tight(the threads) I think NPT is cut on a taper or something. Also you can use a Cummins oil drain plug but I went to a hyd repair shop and they have all you would need to use it for a boost reading. I got a plug and plug with threads in it for another fitting(don't know waht its called) and another part all for less than $7. It took me longer to find the specs online than it did to do the Mod.