Screw Thread Adapters Using Actual Diameters

last year

last modified: last year

I need a screw thread adapter that goes from 1/2 inch (7/16 inch would be better) male to 1/4 inch female. I just learned the hard way that NPT adapters use a nominal dimension. Even 1/8 inch NPT is 0.405 inch actual diameter, so it is too large for my application.

What system supports screw thread adapters using actual measurements? How should I be specifying the part? Is there a particular vendor who would be best for helping to locate the part?

I want to try 3/16 male NPT to 1/16 female NPT, just to see how close that gets me. Who is likely to have that part?

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PRO

PPF.

last year

Search for threaded bushing.

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Comments (12)

A Mat
last year
Pipe (npt) or fastener (tpi) ?
westes Zone 9b California SF Bay thanked A Mat
westes Zone 9b California SF Bay
Original Author
last year
So I have a table showing actual dimensions using nominal NPT sizes. TPI deals with the threading spacing? That's beyond the scope of what I need to worry about for now. I want to just find a way to get the diameter right to start.
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KR Nuttle
last year
It may help to know what you are trying to do? Knowing what you are doing may help with additional suggestion out side of the scope that you presented that would work for you.
westes Zone 9b California SF Bay thanked KR Nuttle
westes Zone 9b California SF Bay
Original Author
last year
@KR Nuttle I need to mechanically connect parts. I do NOT need a pipe fitting and I am NOT working with fluids.
KR Nuttle
last year
Are you measuring the piece in inches when it is actually machined in centimeters?

1 centimeter = .4 inches
westes Zone 9b California SF Bay thanked KR Nuttle
PRO
PPF.
last year
You still need to explain what you are trying to do.

"I need to mechanically connect parts" doesn't tell us enough.
westes Zone 9b California SF Bay thanked PPF.
w0lley32
last year
you might want to look at UNC and UNF thread charts. 1/2-13 UNC and 1/2-20 UNF are common sizes, and the 1/2 is the actual diameter before threading. 1/4-20 UNC and 1/4-28 UNF are also common sizes.

A place like Fastenal or Grainger might be a good place to find help, though you might have to buy a minimum quantity.
westes Zone 9b California SF Bay thanked w0lley32
westes Zone 9b California SF Bay
Original Author
last year
last modified: last year
PPF can you post a URL to buy the exact part whose photo you attached to your last post?

I have a decorative piece I am attaching to a board. The board has a female 1/2 - 13 TPI screw socket. The decorative piece has a 3/8 - 16 TPI male screw. I want to join them together. The part you show would work PERFECTLY. I just need to see what sizes the supplier supports.
westes Zone 9b California SF Bay
Original Author
last year
Once I searched on threaded bushing many options appeared, even on low-end sites like the Home Depot website. Strangely enough, Amazon had more problems and kept pushing me toward pipe fittings and NPT.
w0lley32
last year
last modified: last year
It looks like McMaster-Carr has them in various finishes.
westes Zone 9b California SF Bay thanked w0lley32
westes Zone 9b California SF Bay
Original Author
last year
PPF, I searched threaded bushing and Home Depot sold me yet another pipe fitting with nominal sizing. So either a) threaded bushing is not a term to uniquely describe a mechanical adapter, or b) no one uses terms correctly.