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I have a standard European travel adaptor. What are the two circled holes on the top and bottom for?

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All the middle holes are there for accepting various types of ground (earth) pins.

Specifically, the top two holes are there for British plugs (BS 546, BS 1363), while the bottom two are there for Brazilian, Danish and Swiss plugs. As always, Wikipedia has the gory details:

https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets

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    The lower part of the upper hope looks like it would accept a US plug.
    – phoog
    Jan 14, 2019 at 20:11
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    If this adapter accepts a Danish grounded plug, the ground pin would surely go in one of the top two holes, probably the topmost.
    – hmakholm left over Monica
    Jan 14, 2019 at 22:42
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    It's not entirely accurate to decribe BS546 plugs as "British". Obviously, it is a British standard but these plugs have been obsolete in the UK for decades. A friend of mine had to use them in a university hall of residence 25 years ago and they were staggeringly anachronistic even then. They are used in various other countries, though.
    – David Richerby
    Jan 14, 2019 at 23:52
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    @DavidRicherby the 2A version is still used on lighting circuits and the 5A and 15A for stage lighting (at least dumb incandescent lamps) in the UK. But as regards travel, you're right that they're more common in Commonwealth countries
    – Chris H - UK
    Jan 15, 2019 at 9:39
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    @MartinBonner OK. But it's very unusual to have plug-in lamps controlled by the light switches. Most people who live in the UK will have never seen one of these sockets.
    – David Richerby
    Jan 16, 2019 at 11:40
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Those circled holes will be for various plug style's grounds, however --

That is not a standard socket.

That is entirely an invention of the Chinese junk sellers.

It has not been approved by any competent testing laboratory, and it definitely never will. This type of socket is simply trying to adapt too many kinds of plugs, at the expense of safety, and it would not be able to be listed even if it was made by a competent builder. As such, the junk sellers don't even try to make a safe product. Hence the "for export only" sticker: export it to a jurisdiction we're not responsible for.

Use a listed adapter made for your specific plug-socket pair.

Note that UL, CSA, TUV, SGS, NTL, ETL etc. are marks of reputable testing agencies. CE is not a testing agency, nor is it reputable, as it allows manufacturers to self-test and self-certify, which turns the mark into “Chinese Excrement.” Relevant to electrical since so most of the world harmonizes to rules like US NEC, which require electrical equipment to be certified by a recognized testing lab. CE won't ever be one, for obvious reasons.

Hazards of cheapie multi-plug adapter by Big Clive

John Ward on these… And his teardown.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – JoErNanO ♦
    Jan 16, 2019 at 19:45
  • This may be or not be an answer to the question. Your mods have decided it is worth keeping it here.
    – Willeke ♦
    Jul 30, 2019 at 16:30
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    There are adaptors that have exactly this same pattern (I have a few) that are produced by reputable manufacturers. If properly constructed there is no reason for these adaptors to be unsafe.
    – Krist van Besien
    Jul 31, 2019 at 16:43
  • @KristvanBesien Do they in fact have a UL listing, or non-faked listing from other competent recognized testing lab? I would be thrilled to see that, because it would be a new one by me. AFAIK there are reasons it is impracticable to create multi-adapters that are safe, e.g. allowing so many pin shapes makes it unlikely to have enough contact area on any one of them.
    – Harper - Reinstate Monica
    Jul 31, 2019 at 17:26
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    Afaict at least one reputable brand does make make "lots of stuff to schuko" adapters, but I notice the design is very different from the OPs adapter, with a lot more holes, each of which serves only one or two styles of pin. docs-emea.rs-online.com/webdocs/1561/0900766b81561375.pdf
    – Peter Green
    Aug 9, 2019 at 13:46
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Your adapter is designed to acept a wide range of plug types, unfortunately this also tends to mean it accepts none of them well. The "for export only" label doesn't inspire confidence either. That basically means it is shoddy enough that even the country it was made in doesn't consider it safe.

The holes you have circled in red are to accept the earth/ground pins of the aforementioned wide variety of different plug types. Exactly what is hard to tell from the photo but I'm pretty sure at least UK, US and Australian plugs are supported by that hole combination.

Depending on just how crappy the adapter in question is you may or may not find it actually provides an earth connection between the Earth contacts on the Schuko style plug and the earth pin holes in the socket.

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    proper British sockets have a mechanical lock that prevents anything from being inserted into the live and neutral before the (longer) grounding prong makes contact. this is probably absent here too.
    – dlatikay
    Jan 14, 2019 at 21:18
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    @dlatikay Of course it's absent - otherwise US, EU and other plugs wouldn't activate the shutters.
    – user253751
    Jan 14, 2019 at 22:14
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    The plug into the outlet side of the adapter does not have an earth ground prong, so this is definitely circumventing grounding. Plugging a device with a grounded plug into a non-grounded outlet is always unsafe, regardless of adapter quality.
    – le3th4x0rbot
    Jan 14, 2019 at 22:48
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    Schuko style plugs don't use a pin for earthing, they use side contacts. Those side contacts appear to be present on the OPs adapter, whether they are actually connected properly is another matter of course.
    – Peter Green
    Jan 14, 2019 at 23:14
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    This would not suit Australian plugs. The power and neutral in Australian plugs are flat and at an angle. This adapter doesn't look it supports that geometry. And that is without going on about how bad the earth hole looks like.
    – Peter M
    Jan 15, 2019 at 2:53
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Various grounding pins.

Check Wikipedia on plugs and sockets, to see the variation.

I guess it makes a lot of sense to place the holes similar to what people are used to, and as far as I remember from that list (it's been a while since I spend hours reading through it), all plugs have the grounding pin placed symmetrically in relation to the live pins. And that has resulted in that layout.

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