I saw the thread a week or so ago wherein cautions were given regarding using a "tee" fitting at the location of the oil pressure sender; the suggestion was made to unscrew the plug on the oil gallery at the front of the B230 engine block to access that opening instead.

It was indicated that this plug is 1/4" NPT (Nat'l Pipe Tapered); is this indeed the case, or is it a 1/4" ISO 7/1 tapered thread?

From what I gather, the difference is in the thread forms - NPT uses a 60 degree thread angle, with flat root & crest contours, while the ISO uses a 55 degree angle, with rounded root & crest contours. The taper angle is 1 degree 47 minutes in both instances.

I suppose the question should be "Does it really make any practical difference?"... I just want to avoid any problems which may arise from a thread mismatch - I'm in the planning stages of installing a bypass oil filter. I suppose that a liberal application of Permatex #2 would forestall any oil seepage (presuming the thread pitch is the same for both), but I'd rather do it up right by using matching components (I have access to both ISO and NPT).
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Tom Harper ('86 740GLE, '81 VW Rabbit pickup)