Thin open ended spanner: when 3 mm is enough
Updated: 23 October 2026
The ordinary spanner is the right size and still will not sit beside a caliper pin, a radiator tail or a bicycle fitting. A thin open ended spanner is for that gap, and it is a poor tool for a nut that will not move. Prices are amazon.co.uk figures on 22 October 2026. The [open-ended spanner comparison](/hub/hand-tools/open-ended-spanner) holds the wider table. Peter F., DIY and tools editor, used those UK files, an ISO 10102 sample and Haynes. We did not measure thickness. A qualifying purchase can earn a commission at no extra cost to you.
The ordinary spanner is the right size and still will not sit beside a caliper pin, a radiator tail or a bicycle fitting. A thin open ended spanner is for that gap, and it is a poor tool for a nut that will not move.
The ordinary spanner is the right size and still will not sit beside a caliper pin, a radiator tail or a bicycle fitting. A thin open ended spanner is for that gap, and it is a poor tool for a nut that will not move. Prices are amazon.co.uk figures on 22 October 2026. The open-ended spanner comparison holds the wider table. Peter F., DIY and tools editor, used those UK files, an ISO 10102 sample and Haynes. We did not measure thickness. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Stated thickness | Pairs | Named steel | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  YIYEIE YIYEIE 10-piece ultra-thin set | 3 mm stated | 20 sizes, pairs not printed | Chrome vanadium | 7.1 | about £24.29 | View offer |
 Pronese Pronese 10-piece thin set | 3 mm stated | 6×7–24×27 mm printed | Carbon steel | 6.7 | about £25.99 | View offer | |
 Mandouer Mandouer thin 8 mm pair | 3 mm stated | 8 mm, both ends | 30Cr13 stainless | 5.2 | about £6.89 | View offer |
On this page
The gap a normal head cannot enter
Buy thin when a standard head fouls the surrounding part before the jaw reaches the flats. One UK text on the Pronese describes an Audi caliper where the thin tool did not bend. Another refuses hard car use. UK comments on the YIYEIE praise the thin profile for bicycles and tight gaps. One calls the jaw layout poor. Non-UK reviews are not quoted as British experience. Where thin steel sits beside a ring is on open-ended versus combination.
What 3 mm means against the standard
The 3 mm figure is a stated thickness, not a measurement this comparison made and not a strength test. ISO 10102:2018 covers length and maximum head thickness. A public sample puts a 6×7 mm spanner at most 4.5 mm thick. A head stated at 3 mm can sit under that cap and still be untested. Strength is ISO 1711-1 Series C. None of these thin listings print it. Ignore “70% slimmer”, 58 HRC and 345 Nm. They are seller lines.
The thin sets in this comparison
The Pronese I017-10 prints pairs from 6×7 mm to 24×27 mm, carbon steel, 3 mm stated, at £25.99, with 4.6 from 158 reviews. One UK text reports a missing 10×11 mm. One reports chrome peeling. The YIYEIE Y1001 is £24.29, chrome vanadium, 3 mm stated, and it does not print the pairs. The Mandouer listing is two thin 8 mm stainless open-ends at £6.89, with 4.0 from two reviews. One expected 8 mm and 10 mm. Who should skip each set is on best open-ended spanner sets.
Thin is not a flare-nut spanner
A flare-nut spanner wraps more of the hex. A thin open-end still bears on two flats, which is Haynes’ point. A brake or fuel pipe wants the flare-nut tool. One review mentions the short Mandouer pair for brake bleeding. That single report is not a method. Seat the jaw square, pull in line, and stop at the first slip. The pull is on how to use an open-ended spanner. A stated 3 mm head is for a gap, a known pair, and a nut that already moves.
Common questions
When is a thin open-end the right tool?
When a standard head will not enter the gap and the fastener is not a seized, high-torque nut. UK review themes point at calipers, radiator tails and bicycle gaps. One Audi caliper note says the Pronese did not bend. Another Pronese note refuses hard car use. Keep both. If your ordinary spanner already sits square on the flats, a thin set adds cost and less steel for no gain.
Does 3 mm meet a British or ISO standard?
Not on the evidence in these listings. ISO 10102 sets a maximum thickness. The public sample allows up to 4.5 mm on a 6×7 mm spanner, so 3 mm can be under that cap. Being under a maximum is not a certificate, and none of these ASINs print ISO 10102 or BS ISO 1711-1. A Facom seller’s standards line applies to that seller’s claim only. Do not treat 3 mm, hardness or newton-metre bullets as lab results.
Will a thin spanner bend on a rusty nut?
It might, and you should not use the experiment to find out. The files contain no torque test. One UK Pronese review would not load the set hard on a car. One caliper use did not bend. That is experience, not a rating. For a rusty hex, use a ring or a socket if it will fit. A thin open jaw is for a nut you can turn once the head is in the gap.
How is this different from a flare-nut spanner?
A flare-nut spanner wraps more of the nut so a brake or fuel fitting is held on more than two flats. A thin open-end is still an open U, only slimmer. Haynes’ warning about two-point contact still applies. Use the flare-nut tool on pipe nuts. Use the thin open-end on a hex the normal spanner cannot reach, and stop if it slips. The Park Tool OBW-3 is a third thing: a 2.1 mm, 14 mm bicycle brake wrench, not a metric set.
Which kept set prints the pairs?
The Pronese, from 6×7 mm to 24×27 mm, at £25.99, in carbon steel. The YIYEIE lists 20 sizes and does not print the pairing, at £24.29, in chrome vanadium. Choose Pronese when you need to see the contents, and accept the missing-piece report and the chrome-peel report. Choose YIYEIE when you will measure on the day, and do not treat non-UK reviews as British experience. Neither is a full ordinary workshop roll.
Can I use one on a brake pipe?
Use a flare-nut spanner on a brake pipe, not a thin open-end. An open jaw can round a soft fitting, and a rounded brake nut is a poor place to discover that. One review mentions the short Mandouer pair for brake bleeding. That is one person’s report, not a method. If the pipe nut is tight, or you are not sure of the fitting, leave it.
Related pages
Sources
Sources from the research digest, last checked on 22 October 2026.
- HSE, PUWER overview (retrieved 22.10.2026)
- ISO 10102:2018, assembly tools for screws and nuts (retrieved 22.10.2026)
- BSI, BS ISO 1711-1:2019 hand-operated wrenches and sockets (retrieved 22.10.2026)
- TED, spanners, citing ISO 3318:2016 (retrieved 22.10.2026)
- Haynes UK, car maintenance tools (retrieved 22.10.2026)
- Faithfull compression fitting spanner, 15 mm and 22 mm (retrieved 22.10.2026)
- Monument 15 mm and 22 mm compression fitting spanners (retrieved 22.10.2026)
- Teng Tools 6211, trade double open-end set (retrieved 22.10.2026)