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Discussion Starter · #1 ·
hey guys i bought a new aluminum transmission deep pan and autometer gauge and i was wondering what size NPT tap and drill bit should i use to drill and tap the pan for the gauge fitting. thanks for your replies.
 

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russlaferrera
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Guys, please forgive me! If the fitting is smaller than your pinky it is probably a 1/8 NPT, if it the same size as your pinky it is probably 1/4 NPT , if it is the size of your ring finger it is probably 3/8 NPT, if it is the size of your thumb it is probably 3/4 NPT. If your fingers are close to my size this will be close call.

Or You can reread the directions, and see if they tell you the size, or bring the part to the store and match it up...russ
 

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russlaferrera
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gm_71chevelle said:
well i figured out its 3/8 so i read you should use a 9/16 drill bit and then tap it with a 3/8 NPT tap right? i just dont want to mess this pan up
NO!.... You have a 1/8 NPT. The tap drill is a letter drill "R". Be sure to check the size BEFORE you drill. I am 99% sure of the size.

NOTE: Tubing is measured on the outside. Pipe is measured on the inside (what flows in it) This is why it looks that the numbers are wrong. You measured the Outside, when the inside measurement is what the industry goes by....russ
 

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Time is short, are you ready?
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You most likely have an 1/8 NPT sender.

Maybe looks similar to this:


Here's how I installed mine:



EDIT: I bought my tap at Lowes. It will tell you exactly what size drill bit you need for that particular size tap. Chances are you will not have it in your box!

Good luck, Ed

www.edgesz28.com
 

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russlaferrera
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203 Posts
gm_71chevelle said:
well my gauge mechanical and i read somewhere that they are 3/8 and that 1/8 is electrical. thanks
Take the fitting to the store and match it to a tap. BE SURE!

Draw 2 lines on a piece of paper 9/16 wide, put your fitting between the lines. Your fitting should cover the lines on both sides.

A "R" drill measures .339, 3/8 is .375. A 9/19 drill measures .562 this is too big. You stated the fitting is about 3/8 (.375) a "R" drill is about .375. I hope I do not "cornfuse" you any more....russ
 

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Discussion Starter · #12 ·
thanks that cleared it up really well. So i should most likely use an "R" sized drill bit for 3/8 and ill use some motor oil to lube it up. Im familiar with the technique for tapping and what not, im just not real sharp on sizes haha. I really appreciate it.
 
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