Seven screw head types — pan, truss, binding, countersunk: which to use when
Choose a head by bearing area, protrusion and whether a countersink is possible. Even at M4, head diameter ranges from 6.0 to 9.4 mm.
The head of a machine screw is chosen by three design conditions, not by looks.
- How wide must it bear? — thin sheet or plastic needs a wide head.
- How far may it protrude? — under covers or moving parts use a low head; flush surfaces need a countersunk head.
- Can the part be countersunk? — countersunk heads need a conical seat machined in the mating part.
At a glance
| Head | Shape | Typical use | Countersink |
|---|---|---|---|
| Pan | Gently domed top, flat bearing face | General assembly | No |
| Truss | Wide and low | Thin sheet metal, plastic, slotted holes | No |
| Binding | Narrower than truss, wider and lower than pan | Inside electronics, PCBs and brackets | No |
| Pan with washer | Pan head with integral washer face (in-house standard) | More bearing area without a loose washer | No |
| Flat countersunk | Flat top, conical underside | Flush finish | Yes |
| Small flat countersunk | Smaller diameter and height than flat (in-house standard) | Where the countersink must be smaller | Yes |
| Raised countersunk (oval) | Conical underside, domed top that stands above the surface | Visible hardware such as hinges and handles | Yes |
Same size, different heads — dimensions
Head dimensions from our production drawings (mm, head diameter / head height). Even at M4 the diameter ranges from 6.0 to 9.4 (head body; the washer diameter of pan with washer is shown in brackets).
| Size | Pan | Truss | Binding | Pan w/ washer | Flat | Small flat | Raised csk |
|---|---|---|---|---|---|---|---|
| M3 | 5.5 / 2.0 | 6.9 / 1.8 | 6.3 / 1.95 | 5.5 / 2.2 (washer 7.1) | 6.0 / 1.75 | 5.0 / 1.4 | – |
| M4 | 7.0 / 2.6 | 9.4 / 2.5 | 8.3 / 2.5 | 7.0 / 3.0 (washer 9.1) | 8.0 / 2.3 | 6.0 / 1.4 | 8.0 / 3.2 |
| M5 | 9.0 / 3.3 | 11.8 / 3.1 | – | 9.0 / 3.5 (washer 11.0) | 10.0 / 2.8 | 8.0 / 2.0 | 10.0 / 4.0 |
| M6 | 10.5 / 3.9 | 14.0 / 3.7 | – | – | 12.0 / 3.4 | – | – |
From our production drawings (cross-recessed machine screws, KS B 1023 annex dimensions; pan with washer and small flat countersunk are in-house standards). "–" = not stocked in that size. Full dimensions are in the "Dimensions" table of each product data sheet.
※ For pan with washer, the head diameter is that of the pan head above; the integral washer that bears on the joint has its own diameter (in brackets). Check it when looking at bearing area and clearance.
※ Head height is a dimension of the part, not the height that stands above the surface after assembly. Pan, truss and binding heads sit fully above the surface; a flat countersunk head can sit flush with a correct countersink; a raised countersunk head still stands proud by its dome. The final height depends on the countersink angle and depth, so check it on the assembly section.
- Truss is about 1.3 times the diameter of pan at nearly the same or slightly lower height — it spreads the same clamp load over a larger area.
- Binding sits between pan and truss in width, at the height of truss — an alternative when truss is too wide for neighbouring parts.
- Small flat countersunk is 1–2 mm smaller in diameter and lower than flat, so the countersink is smaller and shallower. Its bearing area may also be smaller, so check the required clamp force and the thickness and strength of the mating part.
How to choose
- Must it sit flush? — if the head must not protrude, consider a flat countersunk head. If a domed top may stand proud for appearance, a raised countersunk head can be chosen. Where countersink space is tight, consider small flat countersunk.
- Is the mating material thin or soft? — sheet metal or plastic: truss; binding if side space is tight.
- Are you adding a loose washer? — pan with washer removes one part and one assembly step.
- No special condition? — pan head.
- Check height and clearance on the drawing — use the head heights above and the data sheet to check covers and cables. Every item has a 3D model for fit checks.
Head types in our catalog (cross-recessed machine screws)
| Head | Catalogue items | Browse |
|---|---|---|
| Pan | 398 | Pan head |
| Flat countersunk | 376 | Flat countersunk |
| Truss | 212 | Truss head |
| Small flat countersunk | 50 | Small flat countersunk |
| Pan with washer | 46 | Pan with washer |
| Binding | 38 | Binding head |
| Raised countersunk | 17 | Raised countersunk |
The same heads are available on tapping screws and SEMS. See tapping screw types and cross-recess driver bits.
FAQ
What is the difference between a pan head and a truss head?
A truss head is about 1.3 times the diameter of a pan head at nearly the same or slightly lower height (M4: pan 7.0/2.6 mm, truss 9.4/2.5 mm). Use truss where a wide bearing area is needed, such as thin sheet or plastic; pan for general assembly.
What do I need to use a countersunk screw?
A conical countersink in the mating part. If the angle or depth does not match the head, it sits proud or tilts. Where the seat must be small, consider a small flat countersunk head.
When is a binding head used?
A binding head is narrower than truss, wider than pan and low. It is common inside electronics — PCBs, covers and brackets — where space is tight and load must be spread evenly.
References
- KS B 1023 Cross-recessed machine screws — head dimensions (we follow the annex)
- ISO 7045 / 7046-1, -2 / 7047:2011 — international standards for pan, countersunk and raised countersunk heads (7046-1 steel 4.8; 7046-2 steel 8.8, stainless A2-70, non-ferrous)
- JIS B 1111:2017 annex JA — conventional screws outside ISO (counterpart of the KS annex)
Last revised 2026-10-12