
Williams is part of the Snap-On family so you know it's good. Exactly what the description says: 5.5mm hex, although by 'flat' it seems they mean thin walled, not short. My Craftsman 5.5mm is actually about 2mm shorter, but the sidewalls are slightly thicker. When working in tight spaces, wall thickness can make a big difference. The only improvement I would suggest would be to make the size more readable like the newer Husky, Kobalt, Craftsman etc. This earns it fifth place. Star.