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Screw Head and Drive Types
Short answer
Identify the head shape first — whether it sits flush decides which head you need — then the drive recess, which decides the bit. The pairs people actually mix up are Phillips and Pozidriv (Pozidriv has four fine lines between the arms), Torx and hex (six curved lobes versus six straight flats), and Phillips and JIS (JIS is marked with a single dot).
Head shapes
| Head | Sits flush | Profile | Typical use |
|---|---|---|---|
| Countersunk (flat) | Yes | Cone underside, flat top | Anything that must finish level — hinges, hardware, trim |
| Pan | No | Low dome, flat bearing face | General machine screws into tapped holes and sheet metal |
| Button (dome) | No | Tall rounded dome, small footprint | Socket-drive fixings where the head is visible |
| Oval (raised countersunk) | Yes | Cone underside, domed top | Flush fixing that still shows a rounded head |
| Socket cap | No | Straight cylindrical head, hex socket | High-torque machine assembly, often in a counterbore |
| Hex head | No | Six external flats | Bolts driven by spanner or socket |
| Hex washer (flange) | No | Hex head on an integral washer | Self-drilling screws into sheet metal and roofing |
| Truss (mushroom) | No | Very wide, very low dome | Thin sheet and slotted material needing a large bearing area |
| Set screw (grub) | Yes | No head at all — threaded full length | Locking a pulley or collar onto a shaft |
Drive types and how to tell them apart
| Drive | Common sizes | How to tell it apart |
|---|---|---|
| Phillips | PH0 – PH3 | A plain cross with tapered, rounded slot ends and nothing between the arms. |
| Pozidriv | PZ0 – PZ3 | A cross plus four fine lines at 45 degrees stamped between the arms. A Phillips driver will cam out of it. |
| Slotted | By blade width, e.g. 5.5 mm | One straight slot right across the head. |
| Torx (star) | T6 – T30 on small work | Six rounded lobes. Hex has six straight flats, Torx has six curved ones. |
| Torx Plus | IP sizes | Torx geometry with squarer lobes; a Torx bit fits loosely and rounds it off. |
| Hex socket (Allen) | 1.5 – 8 mm, or inch keys | Six straight flats, no lobes. |
| Robertson (square) | R0 – R3 | A single tapered square recess. Common in Canadian joinery. |
| JIS | JIS 0 – 3 | Looks like Phillips but has a small dot beside the cross. Japanese machinery — a Phillips bit will strip it. |
| Tri-wing / spanner | Assorted | Three-armed pinwheel, or two round holes. Security fixings on consumer electronics. |
Head shape: start with flush or proud
The first question is whether the head has to finish level with the surface. A countersunk head has a cone underside and pulls itself flush into a countersunk or drilled hole; a pan, button or hex head bears on the surface and stands proud.
Getting this wrong is not cosmetic. A countersunk head driven into a flat hole concentrates all its load on the rim of the hole, and a pan head in a countersunk hole never seats at all.
Phillips, Pozidriv and JIS are three different drives
Phillips was designed to cam out under load, which is why the bit climbs out of a tight screw. Pozidriv was designed not to: it adds a second, shallower cross and shows four fine lines stamped at 45 degrees between the arms. A Phillips bit in a Pozidriv screw contacts on the wrong flanks and rounds the recess.
JIS, common on Japanese machinery and cameras, looks like Phillips but has a small dot punched beside the cross. A Phillips bit sits too shallow in it and strips the head, which is why so many old camera and motorcycle screws are ruined.
Torx versus hex versus Torx Plus
Torx has six rounded lobes; a hex socket has six straight flats. Under a poor light they look identical, and a hex key in a Torx recess bears on six small points and shears them.
Torx Plus is Torx with squarer lobes and no taper. A standard Torx bit will enter it with noticeable slop — that slop is the warning, not something to drive through.
Frequently asked questions
How do I tell Phillips from Pozidriv?
Look between the arms of the cross. Pozidriv has four fine lines at 45 degrees to the main cross and usually a "PZ" mark on the packaging; Phillips has nothing between the arms and rounded, tapered slot ends.
What drive is a six-pointed star screw?
Torx, if the six points are rounded lobes. If it has six straight flats it is a hex socket and takes an Allen key. If the lobes look squared off and a Torx bit rattles, it is Torx Plus.
Which screw head sits flush with the surface?
Countersunk (flat) and raised countersunk (oval) heads, both of which have a cone-shaped underside. Set screws sit flush too, because they have no head at all.
Can I drive a Pozidriv screw with a Phillips bit?
It will turn a loose screw and destroy a tight one. The flank angles differ, so the bit contacts near the top of the recess and rounds it out under torque.
Other tools
Would rather just take a photo?
These charts are the same tables the app matches against. Screw Identifier does the measuring for you: photograph the fastener next to a ruler, or measure it on the screen against a calibrated on-screen caliper.
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