drill bit and tap for pyro in manifold
Diesel Enthusiast
Joined: Mar 2010
Posts: 238
Likes: 34
There are essentially two different types of thread (not counting the various thread pitches and sizes) -- straight and tapered. National Pipe Thread uses a tapered thread, which, as 94cummins12V says above, is tapered for sealing. The more you screw a set of pipe threads together, the tighter they get due to the taper. The taps are tapered for just that reason.
If you take a look at the threads on any piece of pipe, you'll see the taper.
The other type of threads are straight (no taper) and yes, it is possible to get pipes that thread into the straight threads also, but that sort needs some other type of seal. Most common is the SAE pipe thread, which generally is used in the hydraulics industry, as it is a stronger thread than NPT. Hydraulic fittings also have a nut and o-ring included somehow into the fittings that fasten into the straight threads to seal them up.
The fitting for a pyro on our turbos is NPT -- tapered pipe of the standard variety, hence the warning to not tap too deep! Best to tap a bit, test the fitting, then if it doesn't go in far enough, turn the tap another turn or two and re-test. Once it goes in too far, it may blow out and never seal at all.
If you take a look at the threads on any piece of pipe, you'll see the taper.
The other type of threads are straight (no taper) and yes, it is possible to get pipes that thread into the straight threads also, but that sort needs some other type of seal. Most common is the SAE pipe thread, which generally is used in the hydraulics industry, as it is a stronger thread than NPT. Hydraulic fittings also have a nut and o-ring included somehow into the fittings that fasten into the straight threads to seal them up.
The fitting for a pyro on our turbos is NPT -- tapered pipe of the standard variety, hence the warning to not tap too deep! Best to tap a bit, test the fitting, then if it doesn't go in far enough, turn the tap another turn or two and re-test. Once it goes in too far, it may blow out and never seal at all.
Diesel Enthusiast
Joined: Mar 2010
Posts: 238
Likes: 34
Q, R, 21/64, 11/32 -- any will work, just be a tad looser or tighter. We're talking a couple thousands of an inch here.
Big deal is how far you run the tap into the hole. I'd use a Q myself. Just because I'm contrarian (and have a Machinery Handbook that says so).
21/64 = .3281"
Q = .3320"
R = .3390"
11/32 = .3437"
Big deal is how far you run the tap into the hole. I'd use a Q myself. Just because I'm contrarian (and have a Machinery Handbook that says so).
21/64 = .3281"
Q = .3320"
R = .3390"
11/32 = .3437"
Last edited by glfredrick; Mar 21, 2010 at 09:59 PM.
Diesel Enthusiast
Joined: Mar 2010
Posts: 238
Likes: 34
Like we all haven't done that...
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Here is a decent set on sale that will get you every drill size you need.
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