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Description
THREAD7/16"-14 UNC
TOLERANCE2A
STANDARDASME B1.1
MATERIALTool steel
UNC 7/16-14 thread ring gauge — GO and NO-GO set
Inspecting an inch thread with no metric equivalent
| TECHNICAL DATA | |
|---|---|
| Thread type | Unified inch thread UNC |
| Thread size | 7/16-14 |
| Threads per inch | 14 TPI |
| Thread pitch | 1.814 mm |
| Nominal diameter | 11.112 mm |
| Tolerance class | 2A |
| Pitch diameter d2 | 9.779 – 9.898 mm |
| Gauge type | Set: GO ring + NO-GO ring |
| Material | Tool steel, hardened |
| Hardness | 58-62 HRC |
| Standard | ASME B1.1 / ASME B1.2 |
| Manufacturer | Varel |
T
GO ring gauge — screwed on by hand along the full bolt thread.
Z
NO-GO ring with a groove in the knurled surface — stops after no more than 3 turns.
The 7/16-14 UNC-2A engraving on the face of both rings indicates the size and tolerance class of the bolt being inspected.
UNC 7/16-14 thread ring gauge checks an external thread in a size for which there is no substitute. The GO ring gauge must screw on by hand over the full thread length, and the NO-GO ring gauge no more than three full turns — this is the ASME B1.2 criterion for inch threads.
The 7/16 inch size is used where 3/8 is no longer strong enough and 1/2 will not fit the design. It is found in clamping hardware for T-slots 1/2 inch wide and in U-bolts securing a leaf spring pack to an axle — on imported trailers, semitrailers and commercial vehicles. This size is stocked less often than the adjacent 3/8-16 and 1/2-13 sizes, which has practical consequences during repairs.
GO/NO-GO inspection of external threads
Three steps and the acceptance criterion per ASME B1.2
1
The GO ring is screwed on by hand, without force, over the entire thread of the 7/16-14 UNC bolt.
2
The NO-GO ring stops after no more than 3 full turns, without forcing.
3
The GO ring passed and the NO-GO ring stopped — the bolt meets class 2A.
Thread inspection in 3 steps
1 GO ring (GO gauge)
Screwed on by hand — passes over the full length
2 NO-GO ring (NO-GO gauge)
Screwed on by hand — no more than 3 full turns
✓ Acceptable thread
Class 2A confirmed
At a pitch of 1.814 mm, the three permissible turns of the NO-GO ring gauge give an engagement depth of 5.4 mm. A U-bolt has a much longer thread, so the full limit can be used here.
GO ring (GO gauge)
It represents maximum material condition — the maximum permissible pitch diameter of 9.898 mm. It checks profile, pitch and diameter simultaneously, because any error in any of these features increases the functional diameter of the thread. On bolts with rolled threads, this ring gauge detects excess material displaced by the rollers.
NO-GO ring (NO-GO gauge)
It represents minimum material condition — the minimum permissible pitch diameter of 9.779 mm. It detects an undersized thread, one that will not maintain preload after tightening. The body may be stamped LO, the historical designation for the NO-GO side of an external thread gauge.
✓ Thread acceptable — GO screws onto the full thread, NO-GO stops.
✗ Thread oversized — GO does not screw onto the bolt.
✗ Thread undersized — the NO-GO ring screws on more than 3 turns.
Why 7/16 inch has no metric substitute
A size that must be restored rather than substituted
A diameter of 7/16 inch equals 11.112 mm. The closest commercially available metric thread is M12, with a diameter of 12.000 mm — almost a millimeter larger. Size M11 exists in ISO tables, but it is not a preferred size and, in practice, neither bolts nor taps are available in it. There is therefore no replacement for a damaged 7/16-14 bolt without enlarging the hole and cutting an M12 thread, which means modifying the design.
This is what makes a gauge valuable for this size. The pitch is easy to calculate: 14 threads per inch means 25.4 divided by 14, or 1.814 mm. The nominal pitch diameter is 11.112 − 0.6495 × 1.814 = 9.934 mm. If the restored thread falls within the 9.779 – 9.898 mm range, the bolt can go back into the machine without modifications. If it does not, an original replacement must be found — and it is better to know this before assembly.
Classes 1A, 2A, and 3A for size 7/16-14
Why this set is class 2A
Comparison of external thread classes
The nominal pitch diameter of the 7/16"-14 UNC thread is 9.934 mm. Classes 1A and 2A have an allowance of 0.036 mm, so their upper limit is below the nominal value. Class 3A has no allowance.
| Class | Allowance [mm] | d2 permissible [mm] | Tolerance zone | Application | Status |
|---|---|---|---|---|---|
| 1A | 0.036 | 9.718 – 9.898 mm | 0.180 mm | Field assembly, threads exposed to impact damage | |
| 2A | 0.036 | 9.779 – 9.898 mm | 0.119 mm | Commercial standard for inch bolts | THIS PRODUCT |
| 3A | 0.000 | 9.845 – 9.934 mm | 0.089 mm | Joints requiring repeatability |
Class 1A can be justified for this size — U-bolts are installed underneath vehicles, in dirty conditions and often after years of service, and the wider tolerance zone of 0.180 mm can allow a thread with impact damage to be assembled. Class 2A remains the catalog standard, however, and is used with 2B nuts.
▲
A stretched thread will pass the GO ring gauge
A U-bolt tightened beyond the specified torque elongates permanently, and its thread pitch increases with it. Such a thread may be undersized rather than oversized, so the GO ring gauge will screw on without resistance and indicate nothing. Only the NO-GO ring gauge detects it by advancing more than three turns. This is a reason to inspect with a complete set, not a single ring gauge.
Set contents and inspection scope
Set contents and scope of ring gauge inspection
INCLUDED IN THE SET:
| ▸ | GO ring (GO gauge) UNC 7/16-14 2A |
| ▸ | NO-GO ring (NO-GO gauge) UNC 7/16-14 2A |
| ▸ | NO-GO ring marked with a groove or dot |
WHAT THEY DO NOT MEASURE:
| ▸ | Thread major diameter — for 2A, this is 10.815 – 11.077 mm and is measured with a plain gauge |
| ▸ | Permanent elongation of the shank after overloading |
| ▸ | Straightness of the U-bolt and spacing between its legs |
Frequently asked questions
Not without modification. The diameters differ by 0.888 mm and the pitches by 0.064 mm — an M12 bolt will not fit a hole tapped for 7/16 inch. Substitution requires enlarging the hole and cutting a new thread, which means modifying the design. The M11 thread, theoretically closer in diameter, is not a commercially available size, and neither bolts nor taps are available for it.
By the thread count, because the nominal diameter is identical for both at 11.112 mm. The coarse UNC series has 14 threads per inch and a pitch of 1.814 mm; the fine UNF series has 20 threads per inch and a pitch of 1.270 mm. Over a length of 25 mm, this gives 14 threads versus 20. The ring gauges for the two versions are not interchangeable.
Most likely, a thread stretched by overloading. The GO ring gauge will screw onto such a thread without resistance because it is smaller than nominal, not larger. Only the NO-GO ring gauge indicates the problem — it will advance more than three full turns. This is typical of U-bolts tightened without a torque wrench.
Two different standards apply. Inch threads are inspected according to ASME B1.2, section 5.2.1, which allows three full turns of the NO-GO ring gauge. Metric threads are subject to ISO 1502, with a limit of two threads. At a pitch of 1.814 mm, three turns correspond to a thread length of 5.4 mm.
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