1/4x32 spark plug

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BRIAN

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Hi all
I am looking for the taping drill size for a 1/4"x32 spark plug thread for my project engine.

I think the thread is unef but i cant find the drill size on any chart??

Thanks in advance, Brian.
 
7/32 or #2 it should be .2195 for a cut tap. If you search 1/4 32 tap drill size in a search engine you can find it for other sizes
 
Thanks Lads
That's what makes this forum so special, if you have a problem someone will always have the answer.
brian.
 
That is the size for a model airplane engine glow plug. Are you building a glow engine?
 
Hi JPMacG.

The engine is a horizontal engine to run on propane 32 bore by 40 stroke.

If you look in members projects the build is under the title of 32x40H Gas Engine.

Thanks for the interest. Brian.
 
Hey Brian, for future reference, here's the formula for figuring tap-drill sizes (for 75% of thread):

Tap drill size = thread nominal major diameter - (1 / TPI)

In your case, you have .250 - 1/32, or .250 - .03125 (let's call it .031). So, your drill size would be .219. But of course, 1 divided by 32 is also the same as a 32nd of an inch - so, that'd be a 32nd under a 1/4, or 7/32.
 
I am looking for the taping drill size for a 1/4"x32 spark plug thread for my project engine.

7/32 .2188
 
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