Torx screws are sized on a T-scale - T10, T25, T50 - and unlike hex sizes the numbers tell you nothing about physical dimensions until you have a chart. This guide lists every common Torx size with its actual measurements, where each size turns up, what the security (tamperproof) variant is, and the near-miss traps between Torx and hex that damage both screw and tool.
Torx sizes chart: T1 to T100
The T-number refers to the six-lobed star profile. The point-to-point measurement is the widest span of the star - useful for identifying an unknown screw with calipers:
| Torx size | Point to point | Where you meet it |
|---|---|---|
| T1-T5 | 0.8-1.4mm | Watches, cameras, phone internals |
| T6 | 1.7mm | Small electronics, laptop internals |
| T7 | 2.0mm | Electronics, hard drives |
| T8 | 2.3mm | Games consoles, laptop casings |
| T9 | 2.5mm | Electronics, small appliances |
| T10 | 2.7mm | Car interior trim, bicycle disc rotors, appliances |
| T15 | 3.3mm | Car trim and fittings, power tools, bike components |
| T20 | 3.9mm | Car exterior trim, garden tools, household fittings |
| T25 | 4.4mm | The most common size: cars, appliances, decking screws, disc rotor bolts |
| T27 | 5.0mm | Car seats and seatbelt fixings, machinery panels |
| T30 | 5.6mm | Car engine covers, bumper fixings, machinery |
| T40 | 6.7mm | Suspension components, larger automotive fixings |
| T45 | 7.9mm | Driveline and chassis bolts, motorcycles |
| T50 | 8.9mm | Larger chassis and suspension bolts |
| T55-T100 | 11.3-22.4mm | Commercial vehicles, heavy machinery |
The nine sizes from T10 to T50 cover almost everything on cars, motorbikes, appliances and household fittings, which is why a 9 piece Torx key set spans exactly that range. Below T10 you are in precision electronics territory; above T50 you are under a lorry.
Security Torx: the centre pin explained
Security Torx (also called tamperproof, pin Torx or anti-tamper) is a standard Torx recess with a pin standing in the centre. An ordinary solid Torx key cannot enter - the pin blocks it. That is the entire point: the fixing resists casual removal, which is why it guards public installations, sports equipment, washroom fittings, vehicle electronics and anything an owner wants left alone.
The counterpart tool is a Torx key with a hole bored in the tip to clear the pin. A security key drives both variants - the hole makes no difference on a standard screw - which is why every key in a HemBorta security Torx set carries the hole on both the short and long arm. One set, every Torx screw, pinned or plain, from either end.
One caution in reverse: if you are specifying fixings meant to stay put, remember that security keys are as easy to buy as this page proves. Tamperproof deters the casual; it does not stop the determined.
Torx vs hex vs the near-miss trap
A Torx recess and a hex socket are different geometries, but worn screws blur the line and the wrong tool sometimes half-fits:
| Torx | Point to point | Nearby hex key | What happens |
|---|---|---|---|
| T10 | 2.7mm | 2.5mm | Hex key turns in the star lobes, strips the recess |
| T25 | 4.4mm | 4mm | Feels engaged, cams out under torque |
| T30 | 5.6mm | 5.5mm | The classic - a 5.5mm hex almost fills a T30 and ruins it |
| T45 | 7.9mm | 8mm | Will not enter cleanly; forcing it damages both |
A hex key in a Torx screw contacts only the tips of the lobes - tiny surfaces that shear off under load, leaving a rounded crater no tool can grip. The reverse (Torx key into hex socket) can work as a last resort on a damaged screw precisely because the lobes bite into the softer flats, but it is a removal trick, not a practice. Match the tool to the recess.
Choosing arm length
The same T10-T50 range comes in three arm lengths, and the choice is about the space around the screw, not the screw itself. Short arms (45-112mm) work behind bumpers and inside appliances where a full-length key cannot swing. Long arms are the everyday choice - more reach into recessed fixings and more torque on stubborn ones, available in rust resistant satin or black oxide sealed under gloss enamel. Extra long arms (up to 222mm) cross deep housings and assemblies - the difference between reaching a buried T30 and dismantling half the machine to get at it.
Frequently asked questions
What Torx size are bicycle disc rotor bolts? Almost always T25, occasionally T30 on some brands. T25 is the single most useful size a cyclist owns.
What size Torx do cars use? Interior trim runs T10-T20; seats and seatbelt anchors are commonly T27-T45 (and safety-critical - torque them properly); engine covers and bumpers T25-T30; suspension and chassis T40-T55.
Is Torx Plus the same as Torx? No. Torx Plus is a later profile with squarer lobes for higher torque transfer. A standard Torx key loosely fits a Torx Plus screw well enough for light duty, but the proper driver differs. If a fixing is marked IP (e.g. 25IP), that is Torx Plus.
Star key, Torx key - same thing? Yes. Torx is the trademarked name; star key and star bit are the generic terms. Security variants go by tamperproof, pin Torx and anti-tamper.
All HemBorta Torx key sets are available on Amazon; each product page on this site links straight to the listing for your marketplace.
