In article ,
"Dave Plowman (News)" wrote:

Slightly confusing as a 1/2 AF
spanner fits a 5/16ths thread.

Unless it doesn't. We often use "small pattern" hex nuts, which have
thinner walls, hence driven with a smaller wrench. (lay Americans have
no idea what a "spanner" is, but when used here it usually quite
specifically means a very thin open-end wrench, often just made of
stamped steel, designed for tight quarters.)