UNC 1" Socket Cap Screw High Tensile 12.9 Self Colour DIN912 UNC, 1" (8 T.P.I.), Coarse Pitch, High Tensile (12.9), Self Colour DIN 912. A little confusing, no?. So, ‘Socket,’ refers to the hexagon shaped indentation found on the top of the fasteners’ head.
eBay