Fastener Head and Drive Types: A Visual Glossary

"Pan head Pozidriv DIN 7985 A2 M5 x 20." Two-thirds of that string is describing the shape and drive of the head. If you know how to decode that, choosing the right screw for a job is suddenly straightforward.

This is a visual glossary of the head types and drive recesses you'll see across the Simfix range, with notes on what each is best for and links to the specific products. If you also want to decode the DIN/ISO/BS codes, see the standards guide.

The two questions: head shape and drive type

Every fastener head answers two separate questions:

1. What does the head look like? (pan, countersunk, button, hex, dome, etc.)
2. How do you turn it? (slotted, Phillips, Pozidriv, hex socket, square)

Same head shape can come with different drive types - e.g. you can get a pan head with a slotted drive, a Phillips drive, or a Pozidriv drive. They're picked for different reasons, mostly about how cleanly the bit grips under torque.

Head shapes

Pan head

A rounded, low-profile dome on top with a flat underside that sits on the surface. The classic "general purpose" head, especially for machine screws and self-tapping screws. Sits proud of the surface - doesn't bury into it.

Standards: DIN 7985 (machine screw, Pozidriv), DIN 7981-C (self-tapping, Pozidriv)

Best for: Sheet metal work, electrical enclosures, light panel assembly, anywhere it doesn't matter if the head sits proud.

Shop: Pan head machine screws, pan head self-tappers, or jump straight to M5 x 16 Poz Pan Machine Screw (DIN 7985) as a starting size.

Countersunk (CSK)

A flat top with a tapered underside that sits flush with the work surface when seated in a matching countersunk hole. Designed to be invisible - the head sinks into the material.

Standards: DIN 965 (machine screw, Pozidriv), DIN 7997 (wood screw, Pozidriv), ISO 10642 (socket csk)

Best for: Any work where the head must not protrude - flush trim, finished joinery, mating surfaces.

Shop: Countersunk wood screws (DIN 7997) for timber and joinery, socket countersunk (ISO 10642) for metal-to-metal flush mount, or 5.0 x 40 Poz Csk Wood Screw as a common decking size.

Button head

A rounded, more pronounced dome than pan - sits much higher above the surface, with a wider footprint. Internal hex (Allen) drive only.

Standards: ISO 7380-1

Best for: A clean, low-profile finish for socket-head fasteners. Common in machine assembly, automotive interior, jig work where customers see the head.

Shop: Button head socket screws or M6 x 16 button head (ISO 7380-1).

Hexagon head (hex bolt, hex set screw)

An external hex profile - six flat faces on the head, turned with a spanner or socket. The strongest, most torquable head shape in common use because the entire head is structurally engaged.

Standards: DIN 933 / ISO 4017 (fully threaded set screw), DIN 931 / ISO 4014 (partially threaded bolt)

Best for: Structural work, heavy mechanical assembly, anywhere you need maximum clamping force and the head being visible isn't a problem.

Shop: Hex set screws (DIN 933), hex head bolts (DIN 931), or M10 x 30 DIN 933 A2 as the most-used workshop size.

Hexagon socket cap (Allen-head)

A cylindrical head with an internal hex (Allen) recess. Compact, recessed-drive, allows very high torque in tight spaces.

Standards: DIN 912 / ISO 4762

Best for: Machine assembly, jig fixturing, automotive, anywhere space is tight or a hex-key drive is more convenient than a spanner. Excellent torque transfer, clean appearance.

Shop: Socket cap screws or M8 x 20 socket cap (ISO 4762).

Cup square (carriage bolt)

A smooth, rounded dome on top with a square shoulder just below the head. No drive recess - the square shoulder bites into wood or pre-cut metal to stop the bolt rotating; you turn the nut at the other end.

Standards: DIN 603 / ISO 8677

Best for: Timber work where the head needs to sit flush from one side and you only have access to the nut from the other. Decking, fencing, structural joinery.

Shop: Cup square bolts (DIN 603) - see them in context in fencing and gates.

Hexagon coachscrew

An external hex head on a wood-screw thread (deep, coarse, single-start). Drives directly into timber with a spanner or socket - no nut at the other end.

Standards: DIN 571

Best for: Heavy timber-to-timber connections - decking joists, pergola posts, garden structures.

Shop: Coach screws (DIN 571), or 6 x 40 coach screw (DIN 571 A2) as a starting size. See them in context in the decking and garden timber range.

Dome (cap) nut

A nut with a closed, dome-shaped top - hides the end of the bolt and gives a clean rounded finish. Typically A4 grade because they're often used in visible finished applications.

Standards: DIN 1587

Best for: Bathrooms, kitchens, balustrades, decorative connections.

Shop: Dome nuts (DIN 1587) or M5 dome nut A4.

Self-drilling hex head

A hex head on a screw with a built-in drill point - punches through steel sheet up to ~3mm without needing a pilot hole. Used for cladding panels, profile roofing, metal-to-metal sheet fixings.

Standards: DIN 7504-K

Best for: Sheet metal roofing, cladding panels, metal-to-metal sheet fastening on profiles up to 3mm thick.

Shop: Self-drillers (DIN 7504-K) or 5.5 x 25 self-driller A2. The roofing and cladding range bundles these with self-tappers.

Drive types (the recess in the head)

Pozidriv (PZ)

A four-armed cross with additional smaller cross marks between the main arms. The dominant drive type on machine screws and wood screws in the Simfix range. More positive grip than Phillips under power-driver torque.

Phillips (PH)

The original cross-recess drive - four arms only. Designed to "cam out" under high torque (a safety feature in the 1930s when impact drivers were less precise). On modern Pozidriv-compatible work, you'll get less reliable grip.

Slotted (flat-blade)

A single slot across the head. Still used on countersunk machine screws for specific aesthetic or service-access reasons but rare in modern construction.

Hex socket (Allen)

An internal hexagonal recess turned by an Allen key. Standard for socket cap, button head and socket countersunk screws. Excellent torque transfer.

Square recess (Robertson)

A square hole - very secure grip but rare outside specialist trades.

External hex

Not a recess at all - the head itself is a hex profile, turned with a spanner or socket. Used on hex bolts (DIN 931, DIN 933) and coach screws (DIN 571).

Matching head shape to job

Quick reference for common scenarios:

• Need a flush finish in timber? Pozidriv countersunk wood screw (DIN 7997)
• Need a flush finish in metal? Hex socket countersunk (ISO 10642) or Pozidriv csk machine screw (DIN 965)
• Need maximum torque, head visible? Hex set screw (DIN 933) or hex bolt (DIN 931)
• Need maximum torque, tight space, clean look? Socket cap (ISO 4762)
• Decorative head visible? Button head (ISO 7380) or dome nut (DIN 1587)
• Fixing into timber with nut on the back? Cup square (DIN 603)
• Heavy fixing direct into timber? Coach screw (DIN 571)
• Through sheet metal? Pan head self-tapper (DIN 7981) or self-driller (DIN 7504-K)

Choosing the grade too

Head type is one decision; material grade is another. Every fastener on this page is available in A2 (304) or A4 (316) stainless steel. The A2 vs A4 guide has the simple decision rule.

Related Simfix guides

• Stainless Steel A2 vs A4 - Which Grade?
• DIN, ISO and BS Standards Explained
• Marine-Grade Fasteners Buying Guide
• DIY vs Trade Pack: When to Buy Bigger