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Best radiator key for a stiff screw or a normal 5 mm pin

Updated: 23 October 2026

You do not need twelve keys. You need the best radiator key for the screw you have, with enough grip to turn it without rounding the square. A short brass pair is enough for an easy modern pin. A stiff screw, or older and newer radiators in one house, needs a longer lever and a second size. Best here means that match, not the highest star line on its own. Prices are the amazon.co.uk capture of 19 October 2026. The full table is the [Bleed key comparison](/hub/diy-supplies/bleed-key). This is not a lab test. If you buy through our links, we may earn a commission at no extra cost to you.

You do not need twelve keys. You need the best radiator key for the screw you have, with enough grip to turn it without rounding the square. A short brass pair is enough for an easy modern pin.

Our top picks

Heatlab Heatlab dual-size radiator key

Best overall

Heatlab Heatlab dual-size radiator key
9.6/10about £6.99
View offer
Nartel Nartel brass radiator keys, pack of 2

Best value

Nartel Nartel brass radiator keys, pack of 2
9.0/10about £3.49
View offer
QUERGO QUERGO brass radiator keys, pack of 2

Alternative

QUERGO QUERGO brass radiator keys, pack of 2
8.8/10about £3.99
View offer
On this page
  1. 1.Best when the screw is stiff or the house is mixed
  2. 2.Best cheap key when the pin is a normal 5 mm square
  3. 3.What not to crown
  4. 4.A towel rail or a cold bottom is a different job

Best when the screw is stiff or the house is mixed

The conditional top pick is the Heatlab dual-size key at £6.99. It is one 17-7 stainless lever, 7.5 cm long and 15 g, with imperial and metric ends, and 4.8 from 1,393 ratings. Reviewers say the longer handle turns tight bleed nipples where a short brass key had already failed. The pin still has to be square. It is a poor buy for one easy 5 mm screw in a tight gap. One note says the metric end is not a perfect fit on every radiator. An 8 mm key is the wrong direction on a small old pin, which is the imperial or metric bleed key page.

Best cheap key when the pin is a normal 5 mm square

When the screw is the usual modern square and it is not stiff, buy a pair that states 5 mm. QUERGO at £3.99 prints a 12 mm socket depth and a 9 mm outside diameter, with 4.4 from 455 ratings. The short body reaches a corner. The wings are too short for a stubborn screw. Goodility, model 5mm BRK 2024, is the other stated 5 mm pair at the same £3.99. Reviews say the metal bends on a stiff screw. QUERGO is the better of the two when you want a depth figure. If either key slips, stop. Nartel at £3.49 is the best value spare, with 4.5 from 1,295 ratings. It does not state a millimetre size. Do not treat it as the best key for a pin you already know is 5 mm.
Heatlab Heatlab dual-size radiator key

Testsieger

Heatlab Heatlab dual-size radiator key
9.6/10about £6.99
View offer

What not to crown

Heatlab’s PlumbShark, model 1111002, is £12.99 with 4.7 from 510 ratings. Reviewers like one piece for bleed, lockshield and a meter box, and say it is bulky in a tight gap. The listing includes a gas-meter test nipple, which is not a household bleed step. Do not pay £12.99 to vent one panel. RDXMAX at £5.99 has 4.7 from only 46 ratings, and a Vine review calls the lockshield claim misleading. The 8 mm pair, the 5-pack and the towel-rail 3-pack have no review line.

A towel rail or a cold bottom is a different job

A towel rail needs its own tip, not a hope that a panel key will do. One key is not best for both unless the pack names a second tip and people have used it. If the top of one radiator is cold, the next job is the bleed, with the heating off. If the bottom is cold and the top is hot, a key will not fix the flow. No figure here is a measured saving on the heating bill.

Common questions

What is the best radiator key if I only have modern radiators?
A stated 5 mm brass pair, if the screw turns without a fight. QUERGO at £3.99 adds a 12 mm socket depth, which Goodility at the same price does not. Skip the £6.99 Heatlab lever when the gap is tight and the pin is easy. Skip any listing that never states 5 mm if you want the size in writing. You still seat the key once, because a line that says most radiators is not a measurement.
What if a small brass key has already bent?
Move to the Heatlab dual-size lever if the square on the bleed screw is still sharp. Reviewers describe that 7.5 cm stainless key turning pins a short brass key would not. Do not add pliers to the bent brass key. That rounds the screw, and then the longer lever spins as well. If the corners have already gone, stop buying keys and have the plug replaced.
Which listing actually states 5 mm?
QUERGO and Goodility, both £3.99. QUERGO also states 12 mm of socket depth and a 9 mm outside diameter. Minimprover states two 5 mm keys inside a £4.94 utility set. Nartel, Equip247uk, RDXMAX and the 5-pack do not state a millimetre. The 8 mm pair states 8 mm, which is not the modern default. Heatlab states imperial and metric without a millimetre drawing.
Does 4.8 from 1,393 ratings mean it fits my house?
It means many amazon.co.uk buyers rated the Heatlab lever highly, and the written reviews talk about stiff and mixed-age pins. It does not mean every radiator in Britain. One review says the metric end is not perfect on every radiator. A rounded screw, a very tight alcove and a towel-rail hex sit outside that result. Fit is the seat on your pin, not the star line.
Is a key with no reviews a contender?
Not for a recommendation. The 8 mm pair, the 5-pack and the towel-rail 3-pack have no customer-review line in the saved listings. They can still be the right shape if you have measured the pin. They are not the best radiator key in this set, because nobody in the file has reported a seat, a bend or a miss. A low price does not promote them.

Related pages

Radiator bleed key buying guide

How to bleed a radiator

Bleed key

Imperial radiator bleed key or a 5 mm metric socket

Bleed heated towel rail: find the valve, then the tip

Sources

Public UK sources from the digest, and the amazon.co.uk shelf prices stored for 19 October 2026. Page updated 23 October 2026.

  1. British Gas: How to bleed a radiator (retrieved 19.10.2026)
  2. Energy Saving Trust: Energy efficient DIY projects (retrieved 19.10.2026)
  3. Energy Saving Trust: Boiler service explained (retrieved 19.10.2026)
  4. Gas Safe Register: Boiler appliance guide (retrieved 19.10.2026)
  5. HSE: Gas domestic FAQs (retrieved 19.10.2026)
  6. HSE: Gas safety checks and who can do them (retrieved 19.10.2026)
  7. Gas Safety (Installation and Use) Regulations 1998, regulation 3 (retrieved 19.10.2026)
  8. Wonkee Donkee: How does a bleed valve work (retrieved 19.10.2026)
  9. Viessmann UK: Bleed a radiator without a key (retrieved 19.10.2026)
  10. Smart Energy GB: How to bleed a radiator (retrieved 19.10.2026)
  11. HHIC: BS EN 442 radiator standard (retrieved 19.10.2026)