US Authors often use thread descriptions which confuse because the UNC standard uses gauge numbers for sizes under 1/4 inch.

It is not immediately clear that for example, a #4-40 UNC designated screw will be a close enough fit for what Australians would know as 1/8 inch Whitworth or a #6-32 UNC designated screw will be a fit for 5/32 inch Whitworth.

Use this table to decipher the US standard.