British Association Screw Thread
The British Association Screw Thread is a standard for small threads up to six millimeters in diameter (0BA), which are largely obsolete today . BA screw connections were mainly used in Great Britain in model and instrument making and are still used there today.
The BA threads complement the Whitworth threads for screws with a diameter of less than a quarter of an inch . The flank angle is 47.5 degrees and the outer diameter and thread pitch are given in millimeters (instead of inches).
| Nominal size | Outer-ø [mm] |
Pitch [mm] |
|---|---|---|
| BA0 | 6.00 | 1,000 |
| BA1 | 5.30 | 0.900 |
| BA2 | 4.70 | 0.810 |
| BA3 | 4.10 | 0.730 |
| BA4 | 3.60 | 0.660 |
| BA5 | 3.20 | 0.590 |
| BA6 | 2.80 | 0.530 |
| BA7 | 2.50 | 0.480 |
| BA8 | 2.20 | 0.430 |
| BA9 | 1.90 | 0.390 |
| BA10 | 1.70 | 0.350 |
| BA11 | 1.50 | 0.310 |
| BA12 | 1.30 | 0.280 |
| BA13 | 1.20 | 0.250 |
| BA14 | 1.00 | 0.230 |
| BA15 | 0.90 | 0.210 |
| BA16 | 0.79 | 0.190 |
Over 100 years before the conversion to the metric system, the BA threads were based on metric dimensions. It is a pointed thread, but with rounded peaks and valleys. The gradients follow a geometric series: They each correspond to 0.9 times the gradient of the next larger size (smaller identification number), rounded to two places. The flank steepness and thread depth were set uniformly based on the Swiss Thury thread at the fixed values of 47.5 ° and 0.6 times the pitch.
See also
literature
- BS 93: 2008 standard