BS3621, TS007, SS312 Diamond, the Kitemark, Sold Secure, Secured by Design — the marks stamped on a lock are an alphabet soup, and manufacturers cheerfully sprinkle words like “anti-snap” and “3-star” around as though everyone knows what they mean. Most people don’t, and the system genuinely is confusing. This is the plain-English decoder: what each mark actually certifies, and which ones you need for your door.
Because locksmithing and lock-making are not tightly regulated, anyone can describe a product however they like. “Anti-snap” is a description, not a certification — a manufacturer can print it on a box that has passed no test at all. What separates a genuine claim from marketing is independent certification: a recognised body has tested the lock against defined attacks and put its name to the result. Insurers and the police rely on exactly these marks, which is why they are worth learning.
The BSI Kitemark (the little heart-shaped symbol) is the one to recognise first. It means the British Standards Institution has independently tested and certified the product — not merely that the maker says it complies. That distinction matters: a lock marked “BS EN…” with a Kitemark has been tested by a third party, whereas one marked only “EN…” has often just been self-declared. You will find the Kitemark stamped on a lock’s faceplate or engraved on a cylinder.
This family covers complete locks (mortice locks and rim nightlatches) on final exit doors:
On a uPVC or composite door the security lives in the euro cylinder, so it has its own marks. BS EN 1303 classifies cylinders by an eight-digit code covering durability, key security and attack resistance. TS007 is a technical specification (from the Door & Hardware Federation) that rates cylinders and door furniture from one to three stars — and it works as a mix-and-match: you reach the full three stars either with a 3-star cylinder on its own, or by pairing a 1-star cylinder with 2-star handles/escutcheons. SS312 Diamond is Sold Secure’s anti-snap standard, testing the cylinder specifically against snapping; a Diamond cylinder is a top-tier anti-snap part in its own right. For the snapping problem itself, see our anti-snap locks guide, and for the component, euro cylinders explained.
On a timber door: a BS3621 lock carrying the Kitemark. On a uPVC or composite door: a TS007 3-star or SS312 Diamond cylinder. Get those right and you have cleared the bar that matters for both security and insurance.
A few more marks turn up around the home. Sold Secure grades padlocks, chains and the like as Bronze, Silver, Gold and Diamond (ascending), and CEN grades padlocks roughly 1 to 6 — both worth knowing for shed and garage security. Secured by Design is the police-backed accreditation scheme; it carries real weight with insurers and is increasingly specified on new builds. PAS 24 is an enhanced attack test for complete doorsets and windows. None of these replaces the door-lock marks above — they sit alongside them.
You can audit your home in a few minutes. On a timber door, look at the lock’s faceplate on the door edge for the Kitemark and a “BS3621” marking with a year. On a uPVC or composite door, look at the cylinder for engraved stars, a Kitemark or a Diamond. No markings at all usually means the lock is uncertified — and possibly not what your insurer assumes you have, as our guide to locks and home insurance explains. If in doubt, a locksmith can identify any lock in minutes.
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The marks exist to take the guesswork out of buying a lock — but only if you know how to read them. Every LocksmithLocal locksmith can tell you exactly what is on your doors, whether it meets the standard you need, and fit certified, independently tested locks where it doesn’t. Find your local locksmith for a straight answer.
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