Step By Step Measuring Threads

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Thread & Connector Identification

How To Use This Section

This section is intended as an aid to identifying the most popular threads on hydraulic hose couplings and adaptors, and hydraulic equipment.

BSP, Metric, American and Japanese thread sizes can be very similar. It is important to measure and match every criteria of thread diameter, thread pitch, seating or sealing type (including angle of seats if present) to accurately determine thread type.

Step 1. Investigation

Check for any markings on fitting or equipment which may be a clue to thread type. Country of origin may provide a clue.

  • Europe – Check DIN/BSP
  • UK/Australia – Check BSP
  • America – Check NPT/JIC/UNO/ORFS
  • Japan – Check JIS

All RYCO parts have a unique part number stamped on to aid identification.

Step 2. Visual Inspection

Depending on whether the male or female thread or both are available, different features will aid identification.

  • Are threads parallel or tapered?
  • Is there an O Ring or a washer seal?
  • If cone seats are present are they concave or convex?
  • Type and position on fittings

All RYCO parts have a unique part number stamped on to aid identification.

Step 3. Measure Threads

With a calliper, measure the thread diameter.

  • OD of male threads
  • ID of female threads

Using a thread gauge, determine the number of threads per inch.

If thread gauge is not available, measure pitch from crest to crest of adjacent threads, or count the number of threads in 1/4″ and multiply by four for threads per inch. Chart at bottom of page may assist.

Step 4. Seat Angle Measurement

Using a seat gauge, determine the angle of the seat.

Some fittings have dual seats (eg. JIC 37° & SAE 45°) and some have radiused cone.

Step 5. Conclusion

Match the measurements taken against those in the tables herein that appear to be similar to the coupling under consideration.

A final check can be achieved by mating with an actual coupling of the same thread.





TPI (Threads Per Inch) 28 27 24 20 19 18 16 14 12 11.5 11 8 16.9 12.7
THREAD PITCH (mm) 0,91 0,94 1,06 1,27 1,34 1,4 1,59 1,81 2,12 2,21 2,31 3,18 1,5 2,0