Hex head bolt

ISO 4014 / DIN 931 partly threaded, ISO 4017 / DIN 933 fully threaded

Sizes

M1.6-M64

Drive & head

External hex, turned with a spanner or socket

Materials

Carbon steel, alloy steel, A2/A4 stainless

Strength / grades

4.8, 8.8, 10.9, 12.9; A2-70, A4-80

Hole and pilot guidance

Clearance hole per ISO 273 (close, normal or coarse fit). Usually no tapping needed - a nut goes on the back.

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Machine bases, flanges and steel framework

Through-bolted with a nut where a spanner can reach both ends

In a shear joint the plain shank, not the thread, should cross the joint line.
The dashes and numbers on the head are the strength grade - mixing grades changes the tightening torque.
Steel bolts in aluminium or against stainless can corrode where they touch.