To identify the thread on a stainless steel clevis, measure the major diameter with calipers, find the pitch with a thread gauge, and check the hand with a known nut. A metric size written with no pitch, such as M10, means the standard coarse pitch.
Measure the Diameter, Then the Pitch
Most clevis forks have an internal thread. Thread bolts of known size into it until one runs in freely without slop; that gives the diameter, and the gauge confirms the pitch. On an external thread, close the calipers across the crests instead.
Pitch is the distance between neighbouring thread crests. Press the leaves of a thread gauge into the thread until one sits with no light showing through. Reading the pitch is what separates a coarse thread from a fine one, because both have the same diameter.
Coarse or Fine: Check the Pitch Against the Table
Under the ISO metric thread convention, the coarse pitch is left out of the name, so M12 means M12 x 1.75 and M12 x 1.25 is the fine version. The table shows the coarse pitch for common clevis sizes up to M16, and the fine pitches one published DIN 71752 table lists.
| Thread | Coarse pitch (mm) | Fine pitch in a published DIN 71752 table (mm) |
|---|---|---|
| M6 | 1.0 | none listed |
| M8 | 1.25 | none listed |
| M10 | 1.5 | 1.25 |
| M12 | 1.75 | 1.25 |
| M16 | 2.0 | 1.5 |
If the gauge reads 1.25 on an M10, the part is the fine thread, and a coarse-pitch rod will not fit it. Some sizes have only one pitch in the DIN 71752 dimension table, so a reading that matches neither column points to a non-standard thread or an inch size.
Right-Hand or Left-Hand
A right-hand thread tightens clockwise. To check, once diameter and pitch are matched, start a right-hand nut or bolt: if it screws in, the thread is right-hand, and if it jams or turns the wrong way, it is probably left-hand. Some makers mark left-hand parts with a groove or an L in the model number, but that is a convention, so confirm by testing.
A cylinder rod and its clevis must have the same hand, so a left-hand rod needs a left-hand clevis.
What to Send With the Thread Details
- Major diameter and pitch, or the thread gauge reading
- Right-hand or left-hand, and whether the thread is internal or external
- Thread depth or shank thread length
- A photo of the thread next to a ruler
Conclusion
A clevis thread is fully described by its diameter, pitch and hand. Measure the diameter, read the pitch with a gauge, and test the hand with a nut before you order. If you are looking for a new supplier of stainless steel clevises, send the thread readings or the old part to Profab Machine and we will match the thread or machine it to your drawing.