What's the best high security padlock?
Built to resist serious attack, matched to the risk. When security really matters - insurance requirements, high-value assets, exposed sites — you need a padlock built to resist cutting, drilling and prying. Here are the three we would fit ourselves.
Contents
If you want the toughest lock in this guide, buy the Squire SS65CS Stronghold. It's the only one here rated CEN grade 6, the top of the European scale, and its closed shackle leaves bolt croppers very little to grip. Locking a shipping container? Go for the CISA 28550, which is made for container lock boxes. For sites running lots of locks where you need to control who copies keys, look at the ABUS 37RK range. And for boats, trailers and coastal sheds, the ABUS 90RK/50 is the one that won't rust.
Nothing But Padlocks has advised, guided, and supported a range of businesses and end users in selecting the right insurance-rated padlock for the application they need to secure. Customers often don't look at the CEN rating, or it is ok to be outside in the elements - we help every time.
High security padlocks compared
| Padlock | CEN grade | Shackle | Shackle diameter | Weight | Insurance rated | From |
|---|---|---|---|---|---|---|
| Squire SS65CS Stronghold | 6 | Closed | 13mm | 1,093g | Yes | £159.47 |
| ABUS 37RK Granit Plus closed shackle | 4 | Closed | 11mm or 14mm | 695g to 1,139g | Yes | £151.88 |
| ABUS 37RK Granit | 4 | Open | 11mm or 14mm | 506g to 980g | Yes | £142.15 |
| CISA 28550 | 4 | Sliding (container) | 10mm or 12mm | 800g to 900g | Yes | £131.06 |
| ABUS 90RK/50 marine | 3 | Closed, stainless steel | 10mm | 418g | Yes | £55.76 |
*Prices include VAT and are for the smallest keyed different size. Keyed alike and master keyed versions cost a little more.
Our picks
Best overall: Squire SS65CS Stronghold
This is the heavyweight. At just over a kilo, the SS65CS has a solid hardened steel body and a 13mm hardened boron alloy steel shackle, and it carries CEN grade 6. The closed shackle design means only 19mm of shackle is exposed, which is too little for most bolt croppers to get their jaws around.
Squire says it resists picking, drilling and sawing. The finish has been salt spray tested for over 200 hours, so it copes with outdoor use. You also can't take the key out until the lock is shut, which stops staff walking away and leaving it open.
- Size: 65mm (90mm wide, 112mm high, 32mm deep)
- Price: £159.47 keyed different, £168.65 keyed alike
- Best for: yards, compounds, plant and anywhere the insurer asks for the top grade
We see a range of customers buying this padlock, particularly working farms who are looking to secure their vehicles (tractors, storage tanks and outbuildings).
Best closed shackle from ABUS: 37RK Granit Plus
If you'd rather stay with ABUS, this is the closed shackle version of the 37RK. The shroud around the shackle does the same job as on the Squire, and the steel body has a cataphoretic coating that ABUS rates for 40 years of corrosion protection.
Inside is the ABUS Plus disc cylinder, built to resist drilling, pulling and manipulation, with 250,000 key differs. It comes in 60mm, 65mm and 80mm sizes, and you can have it keyed alike or master keyed.
- Price: from £151.88 (60mm), £209.72 for the 80mm
- Supplied with: two keys (one with an LED torch) and a key code card
- Best for: sites already using ABUS that want a closed shackle
Best for key control: ABUS 37RK Granit
The open shackle 37RK is ABUS's classic high security padlock, made in Germany. The body and shackle are both hardened alloy steel, and ABUS quotes over 6 tonnes of pull resistance. It's CEN grade 4 and meets Swedish insurance standards.
Where it stands apart is key control. The Plus cylinder has more than 250,000 differs, and copies are controlled through the key code card, so nobody can get a spare cut at the local key shop. Master keyed versions let one key open every lock on site.
The open shackle gives you more room (27mm vertical clearance on the 63mm) for thick chain or hasps, but it leaves more shackle exposed than the two closed designs above.
- Sizes: 63mm and 77mm
- Price: from £142.15, £177.98 master keyed
- Best for: multi-site businesses and anyone who needs control over keys
Best for shipping containers: CISA 28550
Container lock boxes need a sliding shackle padlock, and the CISA 28550 is made for them. It has a solid hardened steel body with nickel plating, anti-drill protection and a rekeyable cylinder, so you can change the key without replacing the lock. It's CEN grade 4 and insurance rated.
- Sizes: 66mm and 75mm, so measure your lock box first
- Price: from £131.06
- Best for: shipping containers, storage units and site cabins with a lock box
Best for marine and coastal use: ABUS 90RK/50
Salt air ruins steel padlocks. Give a standard lock one winter on a pontoon and it's seized. The ABUS 90RK/50 has a Titalium body, which is ABUS's own aluminium alloy, with a stainless steel shackle and rust-free parts inside. That's why it keeps working on boats, trailers, pontoons and coastal storage units.
There is a trade-off. It's CEN grade 3, one step below the other locks here. Choose it where corrosion is a bigger risk than a thief with croppers, or where a heavier steel lock would simply rust shut. The closed shackle leaves 22mm exposed, and the six-pin cylinder uses anti-pick mushroom pins. It's also key-retaining, rekeyable and insurance rated.
- Size: 50mm, 418g
- Price: £55.76 keyed different, £61.34 keyed alike, £72.95 master keyed
- Best for: boats, trailers, marinas, harbour sheds and coastal outbuildings
We have delivered many tests with our customers in coastal conditions, and the ABUS 90RK/50 came out on top.
What makes a padlock high security?
CEN grades explained
CEN grades come from the European standard for padlocks, EN 12320. Locks are graded from 1 to 6. A higher grade means the lock held out for longer against a wider range of tools in testing. Grade 6 is the highest available, and grades 4 to 6 are generally treated as high security.
Closed shackle or open shackle?
A closed shackle has a steel shroud that covers most of the shackle. Bolt croppers and saws need something to bite on, and a closed shackle gives them very little. An open shackle is easier to fit through hasps and chain, but more of it is exposed. If cutting is your main worry, go closed.
Body and shackle materials
Look for hardened steel on both parts. Boron alloy steel, like the Squire's shackle, is harder again and resists cutting well. Brass bodies are fine for low-risk jobs but aren't high security, whatever the packaging says.
What will your insurer ask for?
Every insurer writes its own terms, so start with your policy wording. Most name either a CEN grade or a Sold Secure rating. If yours just says "insurance approved" without naming a standard, ring your broker before you buy. It's a five-minute call, and it's a lot better than finding out after a claim.
Our high security padlocks and insurance guide goes into this in more detail.
Which one should you buy?
| If you need... | Buy |
|---|---|
| The highest grade available | Squire SS65CS Stronghold |
| A closed shackle and you already use ABUS | ABUS 37RK Granit Plus closed shackle |
| One key for every lock on site | ABUS 37RK Granit, master keyed |
| A lock for a container lock box | CISA 28550 |
| A lock that won't rust on a boat, trailer or coastal shed | ABUS 90RK/50 marine |
Still not sure? Why don't you give us a call or press the button for the live chat widget and ask us the question now?
Frequently asked questions
What is the most secure padlock?
Of the locks in this guide, the Squire SS65CS Stronghold. It's CEN grade 6, the highest grade under EN 12320, and has a closed shackle made from hardened boron alloy steel.
What CEN grade do I need?
If your insurer names a grade, buy at least that grade. If not, grade 4 suits most sheds, gates and compounds. Go for grade 5 or 6 for high-value stock, plant or anywhere that's been targeted before.
Can bolt cutters cut a closed shackle padlock?
They struggle. Croppers need to get their jaws around the shackle, and a closed shackle leaves very little exposed. The Squire SS65CS has 19mm of clearance, for example. A determined thief with power tools can defeat any lock given time. The aim is to make it slow, noisy and not worth trying.
What's the difference between CEN and Sold Secure?
CEN grades come from the European standard EN 12320 and run from 1 to 6. Sold Secure is a UK testing scheme run by the Master Locksmiths Association, with Bronze, Silver, Gold and Diamond ratings. Some insurers ask for one, some the other, so check your policy.
What padlock is best for a shipping container?
A sliding shackle padlock made to fit a container lock box, such as the CISA 28550. Measure the lock box before you order, as it comes in 66mm and 75mm sizes.
Are high security padlocks weatherproof?
All five locks in this guide are rated for outdoor use. The ABUS 90RK/50 goes further, with a marine rating and a stainless steel shackle. For more coastal options, read our marine grade padlock guide.
More high security padlock guides
- Best high security weatherproof padlocks
- Best high security padlock for marine environments
- High security padlocks and insurance ratings
- The full high security range explained
Our Top 3 Picks
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