10UNF ~ 32tpi ~ overall height 0.219" ~ across flats 0.375".
1/4UNF ~ 28tpi ~ overall height 0.236" ~ across flats 0.438".
5/16UNF ~ 24tpi ~ overall height 0.283" ~ across flats 0.500".
3/8UNF ~ 24tpi ~ overall height 0.347" ~ across flats 0.562".
1/2UNF ~ 20tpi ~ overall height 0.458" ~ across flats 0.750".
tpi = threads per inch.