Hartlebury Garage
Old Worcester Road
Hartlebury
Worcestershire
DY11 7XH
England
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Threads
Which Thread?
The biggest problem for many people is to identify sizes of nuts and bolts. Diameter and length are easily established, but to identify the thread itself, a threadpitch gauge is the surest way, used in conjuction with the thread chart.A good steel rule can be used as illustrated below to measure thread pitch. Imperial threads are referred to by threads per inch, and metric by the actual measurement between each thread.
| Diameter | BA | UNF | BSF | BSW | UNC | Cycle | Metric | Metric Fine |
|---|---|---|---|---|---|---|---|---|
| 1/8"/BA | 38.5 | - | - | 40 | - | - | M3 x 0.5 | - |
| 3/16"/2BA | 31.4 | 32 | 32 | 24 | 24 | 32 | M4 x 0.7 | (Common examples) |
| 1/4" | - | 28 | 26 | 20 | 20 | M6 | M5 x 0.8 | (Common examples) |
| 5/16" | - | 24 | 22 | 18 | 18 | 26 | M6 x 1.0 | - |
| 3/8" | - | 24 | 20 | 16 | 16 | 26 | M8 x 1.25 | 1.0 |
| 7/16" | - | 20 | 18 | 14 | 14 | 20 & 26 | M10 x 1.5 | 1.25 & 1.0 |
| 1/2" | - | 20 | 16 | 12 | 13 | 20 & 26 | M12 x 1.75 | 1.5 & 1.25 |
| 9/16" | - | 18 | 16 | 12 | 12 | 20 & 26 | M14 x 2.0 | 1.5 |
| 5/8" | - | 18 | 14 | 11 | 11 | 20 & 26 | M16 x 2.0 | 1.5 |
How to measure fasteners
All types except countersunk.