(8) FILLET. For all lengths of screws the form of the underhead fillet shall be optional, as depicted in the illustration above Table 1B, provided it is a smooth and continuous concave curve fairing into the bearing surface of the head, and the screw shank is within the envelope established by the limits for fillet extension, length, and juncture radius specified in Table 1B.
| Nominal Screw Size | F | FL | R | N | |
| Fillet Transition Dia. | Fillet Length | Juncture Radius | Thread to Head Screw | ||
| max. | min. | max. | min. | min. | |
| No. 0 | 0.074 | 0.063 | 0.012 | 0.002 | 0.051 |
| No. 1 | 0.087 | 0.076 | 0.012 | 0.003 | 0.061 |
| No. 2 | 0.102 | 0.090 | 0.014 | 0.003 | 0.073 |
| No. 3 | 0.115 | 0.103 | 0.014 | 0.004 | 0.084 |
| No. 4 | 0.130 | 0.118 | 0.015 | 0.004 | 0.094 |
| No. 5 | 0.145 | 0.132 | 0.017 | 0.005 | 0.107 |
| No. 6 | 0.158 | 0.145 | 0.017 | 0.005 | 0.116 |
| No. 8 | 0.188 | 0.173 | 0.020 | 0.006 | 0.142 |
| No. 10 | 0.218 | 0.202 | 0.024 | 0.006 |
0.160 |
| 1/4" | 0.278 | 0.262 | 0.024 | 0.007 | 0.215 |
| 5/16" | 0.347 | 0.329 | 0.029 | 0.009 | 0.273 |
| 3/8' | 0.415 | 0.398 | 0.034 | 0.012 | 0.331 |
| 7/16" | 0.484 | 0.465 | 0.039 | 0.014 | 0.388 |
| 1/2" | 0.552 | 0.532 | 0.044 | 0.016 | 0.446 |
| 5/8" | 0.689 | 0.664 | 0.054 | 0.021 | 0.562 |
| 3/4" | 0.828 | 0.801 | 0.066 | 0.025 | 0.681 |
| 7/8" | 0.963 | 0.933 | 0.075 | 0.031 | 0.798 |
| 1" | 1.100 | 1.069 | 0.085 | 0.034 | 0.914 |
| 1-1/4" | 1.370 | 1.334 | 0.102 | 0.044 | 1.148 |
| 1-1/2" | 1.640 | 1.602 | 0.119 | 0.052 | 1.391 |