Identification of Metric Threads
How to ID Metric Threads
Parallel or Tapered?
The first thing you should always do when attempting to identify a foreign thread is to determine if it’s parallel or tapered. You can then measure the thread pitch in millimeters by using gauges overtop of the thread crests. For example, this could be 1.5 millimeters. Once this is completed you can proceed to the next step.
Metric Thread Callout System
For parallel threads, the next thing to do is to identify the thread O.D (outer diameter) by use of calipers (for tapered threads, see next section). Once you identify the O.D of the metric thread you can combine it with the thread pitch to determine the metric thread “callout.” For example, if you identified the thread O.D as 22 millimeters and thread pitch as 1.5 millimeters (from the last example), you would achieve a metric thread callout of M22 X 1.5, or 22mm X 1.5. Refer to the following chart for metric thread “callouts” and their corresponding tube O.D’s, tube nut part numbers, cutting ring part numbers, and tube plug / cap part numbers.
| SERIES | TUBE O.D. | METRIC THREAD | TUBE NUT PART # | CUTTING RING PART # | TUBE PLUG PART # | TUBE CAP PART # |
|---|---|---|---|---|---|---|
| LL | 4 mm 6 mm 8 mm 10 mm 12 mm | 8 mm x 1.0 10 mm x 1.0 12 mm x 1.0 14 mm x 1.0 16 mm x 1.0 | 5201LL-04 5201LL-06 5201LL-08 5201LL-10 5201LL-12 | 5202LL-04 5202LL-06 5202LL-08 5202LL-10 5202LL-12 | ||
| L | 6 mm 8 mm 10 mm 12 mm 15 mm 18 mm 22 mm 28 mm 35 mm 32 mm | 12 mm x 1.5 14 mm x 1.5 16 mm x 1.5 18 mm x 1.5 22 mm x 1.5 26 mm x 1.5 30 mm x 2.0 36 mm x 2.0 45 mm x 2.0 52 mm x 2.0 | 5201L-06 5201L-08 5201L-10 5201L-12 5201L-15 5201L-18 5201L-22 5201L-28 5201L-35 5201L-42 | 5202-06 5202-08 5202-10 5202-12 5202-15 5202-18 5202-22 5202-28 5202-35 5202-42 | 5203L-06 5203L-08 5203L-10 5203L-12 5203L-15 5203L-18 5203L-22 5203L-28 5203L-35 5203L-42 | 5204L-06 5204L-08 5204L-10 5204L-12 5204L-15 5204L-18 5204L-22 5204L-28 5204L-35 5204L-42 |
| S | 6 mm 8 mm 10 mm 12 mm 14 mm 16 mm 20 mm 25 mm 30 mm 38 mm | 14 mm x 1.5 16 mm x 1.5 18 mm x 1.5 20 mm x 1.5 22 mm x 1.5 24 mm x 1.5 30 mm x 2.0 36 mm x 2.0 42 mm x 2.0 52 mm x 2.0 | 5201S-06 5201S-08 5201S-10 5201S-12 5201S-14 5201S-16 5201S-20 5201S-25 5201S-30 5201S-38 | 5202-06 5202-08 5202-10 5202-12 5202-14 5202-16 5202-20 5202-25 5202-30 5202-38 | 5203S-06 5203S-08 5203S-10 5203S-12 5203S-14 5203S-16 5203S-20 5203S-25 5203S-30 5203S-38 | 5204S-06 5204S-08 5204S-10 5204S-12 5204S-14 5204S-16 5204S-20 5204S-25 5204S-30 5204S-38 |
Metric Tapered Threads
If you have a metric tapered thread, one would undergo the same initial steps for identification of thread pitch; however, thread O.D can only be identified properly by placing the calipers over the third row of threads from the end of the fitting. Because the thread is tapered, a different O.D will be identified depending on where you place the calipers; this is why the 3rd row of threads is used as a standard.
Identifying Tube O.D.
If you are using a metric thread for tube application, it is very important that you identify the tube O.D, as this can affect what fitting assembly is used. Simply use a set of calipers to take a measurement of the tube, making sure the results are displayed in millimeters. Then refer to the previous chart to properly determine the thread callout and the related accessories that go with your tube assembly.
Identifying 24° DIN / bite type Tube Fittings
.jpg "Some 24° metric fitting accessories have the dimensions marked on the part.")
Identifying accessories for a 24° compression fitting assembly can be fairly confusing. Some 24° metric fitting accessories have the dimensions marked on the part itself, such as a tube nut for example. Once again, you can refer to the chart provided for examples of sizes and their corresponding assemblies.
A common problem is the inability to distinguish which series is being used or should be used. If the series is not listed on the part, match the tube O.D with the metric thread callout on the chart provided to find the corresponding series.
Kobelco Threads
Kobelco threads are essentially the same as metric threads, with some minor variations. All sizes of Kobelco threads have a 1.5mm (millimeter) pitch. All tube accessories for Kobelco fittings belong to the L-series (for medium pressure).
Komatsu Threads
Komatsu fittings have 1.5mm metric threads with a 30° seat. Tube application is not possible.