BS 450 Machine Screws and Machine Screw Nuts
BS 450:1958 covers machine screws and machine screw nuts with BSW and BSF threads. This table presents selected dimensions for slotted 90° raised-countersunk head screws.
Selected BS 450 Table 3 dimensions
| Nominal size d (in.) | Basic thread diameter (in.) | BSW TPI | BSF TPI | Head dia. dk max. (in.) | Head dia. dk min. (in.) | Head height k max. (in.) | Slot width n max. (in.) | Slot depth t nominal (in.) |
|---|---|---|---|---|---|---|---|---|
| 1/8 | 0.1250 | 40 | — | 0.219 | 0.201 | 0.056 | 0.039 | 0.047 |
| 3/16 | 0.1875 | 24 | 32 | 0.328 | 0.307 | 0.084 | 0.050 | 0.071 |
| 7/32 | 0.2188 | — | 28 | 0.383 | 0.360 | 0.098 | 0.055 | 0.083 |
| 1/4 | 0.2500 | 20 | 26 | 0.438 | 0.412 | 0.113 | 0.061 | 0.095 |
| 5/16 | 0.3125 | 18 | 22 | 0.547 | 0.518 | 0.141 | 0.071 | 0.120 |
| 3/8 | 0.3750 | 16 | 20 | 0.656 | 0.624 | 0.169 | 0.082 | 0.144 |
Note: All dimensions are in inches; TPI means threads per inch. Selected Table 3 values are shown. BS 450 also covers other screw head styles and additional sizes.