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Convert threads and find matching parts
Enter or measure the size: you see SAE, UNF, inches and millimetres at a glance, together with the matching flare nuts, unions and adapters from our range.
- SAE, UNF, NPT and metric threads
- Full-size sizing template to print
- Matching parts with prices
Not sure about the nut, union or adapter?
Tell us the values you measured or send us a photo of the connection. We will tell you which part fits.
A service of H + H Kältetechnik GmbH, Laer, Germany – specialist wholesaler for refrigeration and air conditioning since 2008.
For reference
All dimensions in millimetres, 1 inch = 25.4 mm. Click a circle on the template to use that size in the finder above.
Full-size sizing templateto print
Hold the male thread against the circles: the circle it fits into exactly gives you the size.
Check the scale before measuring. Place a bank or credit card against the frame. If it matches exactly, the size is correct. On screen, reset the zoom with Ctrl + 0 (Mac: Cmd + 0); when printing, set the scale to 100 %, not “fit to page”.
Imperial flare connections (SAE / UNF)
Tapered pipe thread (NPT)
NPT gets narrower towards the end: measure at the first full thread. The designation is the nominal pipe size, not the diameter: 1/4" NPT measures about 13.6 mm.
If the thread fits a dashed circle and is visibly tapered, you need an NPT adapter. It cannot be converted to SAE or UNF.
The template deliberately does not adapt to the screen width. On a phone, swipe sideways.
Thread gauge: threads per inch
Each bar is exactly 1 inch (25.4 mm) long, each line is one thread. Hold the thread lengthways against it: the bar whose lines match the grooves gives you the threads per inch.
Table: convert SAE to UNF
| SAE | UNF | Outside Ø | Minor Ø female | Pipe Ø | Pitch |
|---|---|---|---|---|---|
| 3/16" | 3/8"-24 | 9.525 mm | 8.379 mm | 4.763 mm | 1.058 mm |
| 1/4" | 7/16"-20 | 11.113 mm | 9.738 mm | 6.350 mm | 1.270 mm |
| 5/16" | 1/2"-20 | 12.700 mm | 11.325 mm | 7.938 mm | 1.270 mm |
| 3/8" | 5/8"-18 | 15.875 mm | 14.347 mm | 9.525 mm | 1.411 mm |
| 1/2" | 3/4"-16 | 19.050 mm | 17.332 mm | 12.700 mm | 1.587 mm |
| 5/8" | 7/8"-14 | 22.225 mm | 20.261 mm | 15.875 mm | 1.814 mm |
| 3/4" | 1 1/16"-14 | 26.988 mm | 25.024 mm | 19.050 mm | 1.814 mm |
| 7/8" | 1 1/4"-12 | 31.750 mm | 29.459 mm | 22.225 mm | 2.117 mm |
Table: NPT and metric threads
| Thread | Type | Outside Ø | Pitch | Threads per inch |
|---|---|---|---|---|
| 1/8" NPT | NPT, tapered | approx. 10.272 mm | 0.941 mm | 27 |
| 1/4" NPT | NPT, tapered | approx. 13.572 mm | 1.411 mm | 18 |
| 3/8" NPT | NPT, tapered | approx. 17.055 mm | 1.411 mm | 18 |
| 1/2" NPT | NPT, tapered | approx. 21.223 mm | 1.814 mm | 14 |
| 3/4" NPT | NPT, tapered | approx. 26.568 mm | 1.814 mm | 14 |
| 1" NPT | NPT, tapered | approx. 33.228 mm | 2.209 mm | 11.5 |
| M 10 x 1 | metric, ISO | 10.000 mm | 1.000 mm | – |
| M 12 x 1.5 | metric, ISO | 12.000 mm | 1.500 mm | – |
| M 14 x 1.5 | metric, ISO | 14.000 mm | 1.500 mm | – |
| M 16 x 1.5 | metric, ISO | 16.000 mm | 1.500 mm | – |
| M 19 x 1.5 | metric, ISO | 19.000 mm | 1.500 mm | – |
| M 20 x 1.5 | metric, ISO | 20.000 mm | 1.500 mm | – |
Table: pipe sizes from inches to mm
Measure by the exact value, order by the nominal size.
| Inch | exact | Nominal size |
|---|---|---|
| 1/8" | 3.175 mm | 3 mm |
| 3/16" | 4.763 mm | 5 mm |
| 1/4" | 6.350 mm | 6 mm |
| 5/16" | 7.938 mm | 8 mm |
| 3/8" | 9.525 mm | 10 mm |
| 1/2" | 12.700 mm | 12 mm |
| 5/8" | 15.875 mm | 16 mm |
| 3/4" | 19.050 mm | 18 / 19 mm |
| 7/8" | 22.225 mm | 22 mm |
| 1" | 25.400 mm | 25 mm |
| 1 1/8" | 28.575 mm | 28 mm |
| 1 3/8" | 34.925 mm | 35 mm |
| 1 5/8" | 41.275 mm | 42 mm |
| 1 7/8" | 47.625 mm | none |
| 2 1/8" | 53.975 mm | 54 mm |
Table: cylinder valves according to DIN 477-1
| Gas / refrigerant | Connection no. | Thread | Direction |
|---|---|---|---|
| R32 | 1 | W 21.8 x 1/14" | Left-hand thread |
| R290 (propane) | 1 | W 21.8 x 1/14" | Left-hand thread |
| R22 | 6 | W 21.8 x 1/14" | Right-hand thread |
| R134a | 6 | W 21.8 x 1/14" | Right-hand thread |
| R404A | 6 | W 21.8 x 1/14" | Right-hand thread |
| R407C | 6 | W 21.8 x 1/14" | Right-hand thread |
| R410A | 6 | W 21.8 x 1/14" | Right-hand thread |
| Nitrogen | 10 | W 24.32 x 1/14" | Right-hand thread |
| Oxygen | 9 | G 3/4" | Right-hand thread |
Thread data according to SAE J512, ASME B1.20.1, ISO 261 and DIN 477-1.