Bolt & Screw Head Styles
“What kind of bolt is this?” Match the side profile of the head below to put a name to it — and know what it’s for.
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. Red marks the drive recess.
Turned from the outside (wrench / socket)
Hex
Six-sided head. The everyday bolt — turned with a wrench or socket.
Heavy hex
A thicker, wider hex head for structural and high-strength work (A325 / A490).
Square
Four-sided head — older machinery, set screws, and farm equipment.
Hex flange
Hex head with a built-in washer flange — spreads load, often serrated to grip.
Driven by a recess (sit above the surface)
Socket cap
Tall cylindrical head with a hex socket (Allen) — machinery and tooling.
Button
Low, rounded dome — a finished look with a socket drive.
Pan
Low rounded top with a flat bearing face — the all-purpose machine screw head.
Round
A tall half-dome — a classic, slightly old-style rounded head.
Truss
Extra-wide, low dome — spreads load on sheet metal and soft material.
Fillister
Tall, deep head with a slightly domed top — for counterbored holes.
Sit flush (countersunk)
Flat (countersunk)
Sinks flush with the surface. Measure its length overall, head included.
Oval
Countersunk like a flat head but with a low raised dome — a finished, flush look.
Special
Carriage
Smooth round head over a square neck that locks into wood so it won’t spin.
Eye
A looped head to attach a rope, cable, or hook — for lifting and tie-downs.
What the head tells you
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.