I think you're getting confused. The hex he's refering to is actually the 6mm nut. See the description on the ebay item for clarification.
6mm standard hexagon nut fixing brake calipers
@wvm started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
I think you're getting confused. The hex he's refering to is actually the 6mm nut. See the description on the ebay item for clarification.