I looked it up an apparently a 1/16 npt pipe tap is 6.25mm which is just under a 1/4". I have no idea why its called a 1/16th but that is the correct size. Nos/Holley emailed back and said they couldn't advice me on jet usage for e54 but with them only costing 6$ I'm just going to buy 10 of them and ill have a good setup somewhere in that mix
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