Mechanical decoder
Thread Designation Decoder
Decode ISO metric thread designations such as M10x1.5-6g, M8-6H, and M6x1 LH.
Inputs
Results
- Decoded result
- Waiting for input
- Confidence
- Waiting for input
Segment breakdown
Matched fields
Use the decoder above to read an ISO metric thread designation. Enter the callout exactly as printed: M, diameter, pitch, tolerance class, and any LH suffix. The tool splits diameter, pitch, fit class, and hand into separate fields.
Reference Table
| Input | Decoded result |
|---|---|
| M10x1.5-6g | Metric 10 mm diameter, 1.5 mm pitch, external 6g fit |
| M8-6H | Metric 8 mm diameter, coarse pitch implied, internal 6H fit |
| M6x1 LH | Metric 6 mm diameter, 1 mm pitch, left-hand thread |
Code Structure
| Segment | Meaning |
|---|---|
| M + diameter | ISO metric thread, nominal diameter in mm. |
| x pitch | Thread pitch in mm; omitted means standard coarse pitch. |
| Tolerance class (6g, 6H) | Lowercase for external (bolt), uppercase for internal (nut) threads. |
| LH suffix | Left-hand thread; no suffix means right-hand. |
How To Decode
- Enter the designation exactly as printed, keeping M, x, dash, and LH together.
- Read diameter and pitch first, then the fit class and hand.
- Confirm pitch gauge, length, material, and mating fit in the engineering drawing before manufacture.
Sources And Limits
ISO metric screw thread designation practice and public engineering reference tables; verified 2026-08-26. The callout alone never confirms length, material, coating, or the mating part fit.
Decode logic
- Read the M prefix and nominal diameter first (M10 means a 10 mm metric thread), then the pitch after x when it is printed.
- When pitch is omitted (M8), read the coarse-pitch default from the ISO table; when printed (M10x1.25), the explicit pitch wins.
- Read the tolerance class by case: lowercase 6g marks an external thread, uppercase 6H an internal thread; never swap them.
- Read a trailing LH as left-hand thread, and keep strength, torque, and fit checks on the engineering drawing and standard.
FAQs
What pitch does M8 use when none is printed?
M8 without pitch reads the ISO coarse default of 1.25 mm. An explicit pitch such as M10x1.25 always overrides the default.
Which is the external thread: 6g or 6H?
Lowercase 6g marks an external (bolt) thread and uppercase 6H an internal (nut) thread. Case matters; they are not interchangeable.
How do I read a left-hand thread marking?
Look for a trailing LH such as M6x1 LH. Without LH the designation reads as a standard right-hand thread.
Can I enter a UNC marking here?
No. Markings such as 1/4-20 UNC or G1/2 return an unsupported-system result. Use an inch or pipe thread reference instead.