1/4 NPT makes sense as my bolt size measurer would only go half way up the thread in the 1/2" hole. It's an American throttle cable with a threaded bolt attached. How do you tap out a tapered thread or is the tap the same diameter through it's whole length?
NP & NPT, or it may be NPT & NPTT, cant remember, National Pipe,& National Pipe Taper, then it may be National Pipe Thread, and National Pipe Taper Thread, havent had time to check my boxes of taps yet.
it might be 1/4 npt, that is about 1/2" and 18 tpi. im sure i have 1/4 npt taps in the workshop, i will have a look in the morning, could pop one in the post for you to borrow (cheaper than buying one just for one hole). all it will cost is the postage and a donation to charity.
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