6UNC ~ 32tpi ~ overall height 0.171" ~ across flats 0.312".
8UNC ~ 32tpi ~ overall height 0.203" ~ across flats 0.344".
10UNC ~ 24tpi ~ overall height 0.219" ~ across flats 0.375".
12UNC ~ 24tpi ~ overall height 0.236" ~ across flats 0.438".
1/4UNC ~ 20tpi ~ overall height 0.236" ~ across flats 0.438".
5/16UNC ~ 18tpi ~ overall height 0.283" ~ across flats 0.500".
3/8UNC ~ 16tpi ~ overall height 0.347" ~ across flats 0.562".
1/2UNC ~ 13tpi ~ overall height 0.458" ~ across flats 0.750".
tpi = threads per inch.