Spanner Size Nuts (or “Across Flats” – A/F) refers to the measurement between two parallel sides of a hexagonal nut, determining the size of the wrench needed, not the thread diameter. Common metric nuts range from M3 (5.5mm spanner) to M24 (36mm spanner), with staples like M8 using a 13mm spanner and M10 using a 17mm spanner.