If I want to drill and tap a 1/8 NPT hole in an oil filter take off for a gauge sender what sort of initial hole is required and then how is the thread best cut?

You need a decent thread cut through the whole depth of the hole. I am guessing you can over do this as the tap is tapered and so if you go too deep it will ream the hole to the diameter of the widest / deepest part of the tap.

What is the best size hole and any tips on cutting the tapered thread without going oversize but ensuring that a good thread is achieved throughout the taper.

Bit of a waffle but never cut a tapered thread Might be worrying about nothing but any tips welcome.

What bit / tap do you reccomend?

 

Measure the tap...and drill a hole big enough so you can start the thread.

Then measure the fitting you want to screw in and reference the widest point to the same portion of the tap.

And just make sure you dont screw the tap in any further than that...ideally slightly less to ensure the fitting secures tightly into the hole.

Just hand cut with some sort of lubricant, oil, cutting lube etc. But go slow and remove and test fit the fitting if need be to ensure you dont cut too deep

 

Good tips Steve - like the measuring of the tap V's the fitting

Cheers.

 

For 1/8 NPT thread, drill 8.7mm