The head is how you tell one fastener from another at a glance — and it decides how the fastener is driven and how it sits against the surface. Here are the styles you’ll meet most, drawn from the side, grouped by how they’re turned.
Six-sided head. The everyday bolt — turned with a wrench or socket.
A thicker, wider hex head for structural and high-strength work (A325 / A490).
Four-sided head — older machinery, set screws, and farm equipment.
Hex head with a built-in washer flange — spreads load, often serrated to grip.
Tall cylindrical head with a hex socket (Allen) — machinery and tooling.
Low, rounded dome — a finished look with a socket drive.
Low rounded top with a flat bearing face — the all-purpose machine screw head.
A tall half-dome — a classic, slightly old-style rounded head.
Extra-wide, low dome — spreads load on sheet metal and soft material.
Tall, deep head with a slightly domed top — for counterbored holes.
Sinks flush with the surface. Measure its length overall, head included.
Countersunk like a flat head but with a low raised dome — a finished, flush look.
Smooth round head over a square neck that locks into wood so it won’t spin.
A looped head to attach a rope, cable, or hook — for lifting and tie-downs.
How it’s driven (wrench, socket, screwdriver) and how it sits (proud or flush) both come from the head — and the head style also changes how you measure length. Flush heads (flat, oval) are measured overall; the rest are measured under the head. See how to measure a fastener. To identify the drive recess (Phillips, Torx, square, security), see the drive & security chart.
