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Antique Engine Archives All archived posts from 1999 to 2004 when SmokStak was on EnginAds. This is a read-only board.

Antique Engine Archives

Threads per inch and size of Spark Plugs


What are some of the less common threads used on spark plugs?

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  #1  
Old 10-16-2004, 08:04 AM
Pat Barrett Pat Barrett is offline
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Default Threads per inch and size of Spark Plugs

What are some of the less common threads used on spark plugs?
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  #2  
Old 10-16-2004, 11:46 AM
Jim Tremble
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Default Re: Threads: Spark Plug

1/2" pipe--3/4" pipe and 7/8" straight thread.

Jim
  #3  
Old 10-17-2004, 11:32 AM
Ed Radtke
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Default Re: Threads: Spark Plug

1/4-28 and flange mount
  #4  
Old 10-17-2004, 10:31 PM
Andrew Mackey
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Default Re: Threads: Spark Plug

3/8=20 used on model engines and I understand a '30 s vintage chevrolet auto. The model plug was 1/2" tall, the auto version - 2" or more. 10 and 12 Millimeter metric plugs. The most common plugs - 14mm, 18 mm and industrial - 22mm (7/8") Andrew
  #5  
Old 10-19-2004, 08:33 PM
NICK
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Default Re: Threads: Spark Plug

I have an INFERNO plug that has 1/2 NPTS threads, needs a copper washer to seal too.

Cheers! NICK
  #6  
Old 10-20-2004, 09:53 PM
BobRR
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Default Re: Threads: Spark Plug

OK Nick. Why both? BobRR
  #7  
Old 10-21-2004, 07:02 AM
NICK
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Default Re: Threads: Spark Plug

NPTS threads do not seal like regular NPT threads unless a sealant is used. So there is a shoulder machined on plug body for a copper gasket.

Cheers! NICK
  #8  
Old 10-23-2004, 12:21 AM
Bill Sherlock
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Default Re: Threads: Spark Plug

NPT is a tapered thread, believe the S in NPTS indicates that it is a straight thread so doesn't get tighter as parts are screwed together.

Bill
  #9  
Old 10-23-2004, 09:12 PM
Rob Charles
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Default Re: Threads: Spark Plug

I looked in Machinerys handbook and I didn;t find NPTS.There is a NPTF which is a dryseal thread but thats tapered.There's a NPSI which is a dryseal straight thread.I can't see why that a manufacturer would go thru trouble of making a tapered thread and a shoulder.it's very hard to fit up.All it would take is to be off a 1/8 turn with the tap and the shoulder won't seal.Probably a straight thread to a shoulder it makes more sense. Rob
  #10  
Old 10-24-2004, 07:35 AM
NICK
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Default Re: Threads: Spark Plug

Rob, that was my mistake, that T shouldn't be in there. The plug has NPS threads. I found it very odd that a spark plug would use straight pipe threads and a copper gasket instead of a tapered thread.

Cheers! NICK
  #11  
Old 10-26-2004, 01:15 PM
BobRR
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Default Re: Threads: Spark Plug

Thanks Guys. Seems odd to do it that way!BobRR
 


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