Why are different screw heads used in UK 3 pin plugs?

Looking closely at that picture, I notice that it says "BS1363 GAUGE". Not BS1363A as any modern plug should. I suspect that the "gauge" means that it's made to the dimensions of a BS1363 plug, without ever having been tested for compliance.

As for the screws, It's usual for the terminals to use flat head screws. I suspect that for the rest, they used whatever they had. Looking at other plugs, there seems no consistency.

Looking closely at that picture, I notice that it says "BS1363 GAUGE". Not BS1363A as any modern plug should. I suspect that the "gauge" means that it's made to the dimensions of a BS1363 plug, without ever having been tested for compliance.

As for the screws, It's usual for the terminals to use flat head screws. I suspect that for the rest, they used whatever they had. Looking at other plugs, there seems no consistency.

Simon Barker said:

I notice that it says "BS1363 GAUGE". Not BS1363A

It is not required to mark the plug 'BS 1363/A' ... that is reserved for plugs classified as 'rough use plugs'.

The three possible markings in the current BS 1363-1:2023 (Clause 8.1) are:

• 'BS 1363' (general use plugs)
• 'BS 1363/A' (rough use plugs)
• 'BS 1363/EV' for plugs suitable for EV charging loads (charging modes 1 and 2).

Therefore, the marking meets the requirements of the standard.

Simon Barker said:

without ever having been tested for compliance.

PMS type 8191 plugs appear to be widely used, and, unless it's a fake product, I believe is covered by a Kitemark license that also covers a number of other brands the product is marked and sold under a number of other brands too. Whilst Lisa Miles  didn't post a picture of the cover of the plug, I believe after a little research the plug is covered by BSI Kitemark KM 54406, see:

• https://www.koalacomponents.com/produits/img/upload/homologaciones/AR4950001.PDF
• https://www.bsigroup.com/en-NZ/products-and-services/assessment-and-certification/validation-and-verification/client-directory-certificate/KM%2054406/ 

The PDF of the Kitemark certificate confirms the 8191 is 'normal use' and correctly should be marked 'BS 1363', whereas the 9518 (one of which, coincidentally, I have on my desk as I type) is BS 1363/A 'rough use'. I can confirm the 9518 I have has the Kitemark and license number 54406 on it.

It's not unusual these days, to see, in addition to BS 1363 markings, those of other standards for tine international market, such as IS 401 for the Republic of Ireland, or SS145 for Singapore.

I haven't yet uncovered what 'GAUGE' refers to.

I notice that it says "BS1363 GAUGE"

I wonder if the intention was to distinguish it from "Walsall Gauge"?

   - Andy.

gkenyon said:

I haven't yet uncovered what 'GAUGE' refers to.

Confirmation that it fits the test gauge in Figure 5 of BS 1363-1?

Luckily gkenyon the fan is still out back in my pile of small electronics to take to the recycling plant when I get five mins... 

Here's the cover

I have replied privately.

Ok that confirms it has the BSI kitemark.

Simon Barker said:

Ok that confirms it has the BSI kitemark.

But ... is the Kitemark license number a valid one?:

• The number would usually have a 'KM' prefix
• There don't appear to be enough digits for a BSI-assigned kitemark number that's still valid, but I might be wrong on that one.