3/8 x 20 tap, correct me if I'm wrong

[ddmunroe]

Hi,
What is the background of this tap and where would it mostly finds it uses.
I had to check it 3 times for the pitch and diameter. (It is not marked)
It definately is a 3/8 x 20 tap
Thank's
dd

 

[Don B]

Are you sure it's not a 9 x 1.25 mm?

 

[ddmunroe]

Don,
I don't blame you for asking ..... it got me too when I measured it .... It's .375 20 TPI
Measured with different power glasses to be sure !
These taps must have a specific purpose.
dd

 

[Marco Bernardini]

Are you sure it's not a 9 x 1.25 mm?

9 mm bolts are pretty unusual, in the metric world: generally it's a diameter reserved to handgun bullets :headshot: :biggrin:

3/8" are 9.525 mm: good to tap an 8.80 mm hole for a fine thread M10 ×1.25 bolt… but even those are not very common.
A good table with metric sizes is here.

 

[Ken_Shea]

That's an odd one for me as well, it's listed a UN type thread, UN is designated as "UN bolts and machine screws are the type of fastener in everyday use in the US, UK, and Canada"

Ken

 

[Don B]

Don,
I don't blame you for asking ..... it got me too when I measured it .... It's .375 20 TPI
Measured with different power glasses to be sure !
These taps must have a specific purpose.
dd

Found it in a reference book I have "American national form thread special pitches"

Edit: interesting never payed much attention before these "American national form thread special pitches" seem to split the difference between NF and NC, for instance 1/4-24 and 5/16-20 and so on.

 

[Cactus Farmer]

Non standard taps are quite common in many trades. I gunsmith and have 7/32X40, 1/2X32 8X40 and 6X48 and use them often. Metric sizes were suppose to make it all easier but I find about as many nonstandard sizes in metric as English The odd ones are harder to find in the metric sizes too. I think I even have a 3/8X20 in my collection. Ever hear of a #7 machine screw size? Well I have the taps and die for that oddball too. 1/4X40, 1/4X50 and an assortment of others. I don't always find the taps and die together. If I find it in a sale it may not be there but if I'm buying it new I get both......just easier to have it on hand than have to order it for that "special" job.

 

[Andre]

I have a few bolts (and saw a box at a garage sale yesterday) of 3/8-20 and 1/2-20.

I have a little china jacobs chuck that threads onto 3/8-20. I had to make an adapter to fit my homemade lathe project spindle.