Threaded Holes Standard
Our CNC machining services make it easy to add threaded features to your CNC parts. If the order includes threads, the PO will specify “includes threads.” If not, it will state “no threads” or “does not include threads.” We offer four main types of standard threads for all customers: UNC, UNF, Metric (as defined by ISO 261 and 262), and NPT. Occasionally, we may also offer other types of threads, such as NPS, NPTS, STI, and BSP. Different threads or no threads can be selected for each feature.
If customers request threaded inserts/helicoils, this should be indicated in the specifications and technical drawings. Ensure the required inserts can be met and use the appropriate gauges during inspection.
If you have any questions or concerns, please contact [email protected].
Threads Tolerances
When machining threads, unless otherwise specified on the technical drawings, our standard tolerances should be followed.
We recommend using GO-NOGO gauges (i.e., plug gauges) to check all standard threads, as our quality department will perform control checks.
Metric Thread Tolerances:
Unless otherwise specified on the drawing, metric thread tolerances should comply with ISO 965-1 standards. Standard thread tolerances for commercial external and internal threads are as follows: internal threads are 6H, and external threads are 6g. If the tolerance grade is not specified, it implies the tolerance quality is “medium,” .
UN Thread Tolerances:
Unless otherwise specified on the drawing, UN thread tolerances should comply with ASME B1.1-2003 standards. Standard thread tolerances for commercial threads are 2A for external threads and 2B for internal threads.
Internal Threads:
- 5H is applicable for threads below M1.4 (uncommon).
- 6H is applicable for threads M1.6 and above.
| Internal Thread Tolerance Grades | ||||||
|---|---|---|---|---|---|---|
| Tolerance Quality | Tolerance Position G | Tolerance Position H | ||||
| S | N | J | S | N | L | |
| Fine | — | — | — | 4H | 5H | 6H |
| Medium | (5G) | 6G | (7G) | 5G | 6G | 7G |
| Coarse | — | (7G) | (8G) | — | 7G | 8G |
GO and NO-GO gauges for 6H internal threads.
External Threads
- Threads M1.4 and below are 6h (uncommon);
- Threads M1.6 and above are 6g.
| External Thread Tolerance Grades | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tolerance Quality | Tolerance Position E | Tolerance Position F | Tolerance Position G | Tolerance Position H | ||||||||
| S | N | L | S | N | L | S | N | L | S | N | L | |
| Fine | — | — | — | — | — | — | — | (4G) | (4G5G) | (3H4H) | 4H | (4H5H) |
| Medium | — | 6E | (7E6E) | — | 6F | — | (5G6G) | 6G | (7G6G) | (5H6H) | 6H | (7H6H) |
| Coarse | — | 8E | (9E8E) | — | — | — | — | 8G | (9G8G) | — | — | — |
GO and NO-GO gauges for M12 external threads with 6g tolerance.
