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Subject: Spark plug thread?

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Farmer Dan    Posted 12-12-2018 at 13:50:40 [URL] [DELETE]        [Reply] [Email]  
  • Spark plug thread?
  • I have been laid up for too long. What size drill bit and tap do I need for a standard "N" spark plug? 14mm x 1.25? Are the spark plug threads the same as a common 14mm nut? I think the pitch is diffent if I remember right. Will a spark plug thread into a 14mm nut?

    Tim Daley(MI)    Posted 12-12-2018 at 16:40:16 [URL] [DELETE]        [Reply] [No Email]  
  • Re: Spark plug thread?
  • This chart says use a 12.8mm or 1/2" drill bit for the fine pitch 14mm x 1.25mm tap. Fine pitch threads always use a different tap than their coarser thread counterpart. For example, a 1/2-13 thread size uses a 27/64 (.4219") tap drill and a 1/2-20 thread size uses a 29/64 (.4531") tap drill. The Ford spec'd spark plug, Champion H10, 14mm is the fine thread pitch (1.25mm)type. The coarse thread size would be 1.5mm, a .010" larger pitch. You need the correct 14mm x 1.25mm nut and sure, the H10 plug will screw into it just fine. I have both 14mm taps in 1.25 pitch and 1.5 pitch if you need one. Plenty of drills in both INCH and METRIC sizes as well.

    Tim Daley(MI)

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