Screw Drives & Head Styles

Identify the recess by sight, then pick the driver size from the tables. The lookalikes matter most: Phillips, Pozidriv, and JIS crosses are three different geometries, and using the wrong driver strips the recess.

Drive recess identifier

Slotted One straight slot.

Phillips Plain cross, no extra marks. Wings taper — drivers cam out under torque by design.

Pozidriv Cross plus four tick marks at 45°. A Phillips driver fits badly — use a PZ bit.

JIS cross Japanese standard; often a single dot on the head. Phillips drivers chew it — use a JIS bit.

Hex socket Six flats; driven by a hex (Allen) key, sized across flats.

Torx Six rounded lobes (T-numbers); near-zero cam-out. Security version adds a center pin.

Square (Robertson) Square recess, slight taper; sizes by number and driver color.

Telling the crosses apart: Pozidriv heads carry four tick marks between the wings; JIS screws (common on Japanese equipment and bicycles) often carry a single dot. A Phillips driver in either one grips only partially — it will cam out and strip the recess under torque.

Torx sizes (ISO 10664)

Size	Across lobes (A)	Inches
T1	0.90 mm	0.0354″
T2	0.98 mm	0.0386″
T3	1.10 mm	0.0433″
T4	1.28 mm	0.0504″
T5	1.42 mm	0.0559″
T6	1.70 mm	0.0669″
T7	1.99 mm	0.0783″
T8	2.31 mm	0.0909″
T9	2.50 mm	0.0984″
T10	2.74 mm	0.1079″
T15	3.27 mm	0.1287″
T20	3.86 mm	0.1520″
T25	4.43 mm	0.1744″
T27	4.99 mm	0.1965″
T30	5.52 mm	0.2173″
T40	6.65 mm	0.2618″
T45	7.82 mm	0.3079″
T50	8.83 mm	0.3476″
T55	11.22 mm	0.4417″
T60	13.25 mm	0.5217″

Measure across two opposite lobes to identify an unmarked Torx recess. Security (tamper-resistant) Torx adds a center pin — the same T-number, but it needs a TR bit with a matching hole.

Phillips & Pozidriv driver numbers

Driver	Typical screw sizes
PH0 / PZ0	#0 – #1
PH1 / PZ1	#2 – #4
PH2 / PZ2	#5 – #10
PH3 / PZ3	#12 – #16
PH4 / PZ4	#18 and larger

The conventional pairing — PH2 drives the vast majority of common screws. Pozidriv numbers parallel Phillips, but the recesses differ: match the driver family to the recess, not just the number.

Square (Robertson) sizes

Size	Driver color	Typical screw sizes
#00	orange	#1 – #2
#0	yellow	#3 – #4
#1	green	#5 – #7
#2	red	#8 – #10
#3	black	#12 – #14

Hex socket sizes

Hex (Allen) keys are sized per screw diameter — see the socket head cap screw charts for the key and counterbore for every size, inch and metric.

Head styles

Pan The general-purpose head: flat top, rounded edge, sits proud.

Button Low dome, usually socket-driven; sits proud.

Flat (countersunk) Sinks flush. Inch heads are 82°; metric are 90° — the angles don’t interchange cleanly.

Oval (raised countersunk) Countersunk with a shallow dome above the surface.

Socket cap Tall cylinder with a hex socket; fits a counterbore.

Hex External hex, wrench-driven; the fastener chart’s width across flats.

The countersink trap: inch flat heads (ASME B18.6.3) are 82°, metric flat heads (ISO 2009/7046) are 90°. A metric screw in an 82° countersink bears only at its rim — re-cut the countersink to match the screw.

Data provenance. ISO 10664, Hexalobular internal driving feature for bolts and screws (Torx) (ISO). Conventional driver-size charts (Phillips/Pozidriv numbers, Robertson sizes and colors) (Industry reference). ASME B18.6.3, Machine Screws (head styles and 82° flat head countersink) (ASME). Driver-to-screw pairings are the conventional chart, not a standard dimension — check the recess when it matters. See all data sources.