Is the width of the actual hole 5mm or is that the width of the external diameter please?

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I think you mean 50mm and not 5mm :-)

I am sorry to say the answer is not as simple as you might think though !
Generally speaking the size, if it is in 'metric', it refers to the OUTSIDE diameter of the pipe BUT for 'solvent weld pipe' this isn't the case.

I bought the 32mm and 40mm sizes and used a fully certified vernier calliper to measure both inside and outside of the 2 pipes that I purchased, and the results were as follows :
Stated Size :  32mm      Actual Inside Diameter : 32.34mm      Actual Outside Diameter :  36.35mm  
Stated Size :  40mm      Actual Inside Diameter : 38.40mm      Actual Outside Diameter :  42.82mm  
You will find the 50mm pipe to have to have a similar spec, i.e. the outside diameter will be larger than 50mm and the inner diameter will be about the stated size.

To make things even more confusing, in the UK both metric and inches are used and they are NOT compatible with each other.
In metric 50mm is the OUTSIDE diameter of the pipe, in other words the name is the outside size.
In imperial, the size quoted is the bore diameter. i.e. the INSIDE diameter, imperial was used up until around 1979 (I think) in plastic pipes, then plastic pipe went all metric sized

Pipes like these for solvent welding are used for overflow and drainage and are generally made of either Acetyl Butyl Styrene (ABS) or Poly Vinyl Chloride (PVC) and usually only made in 32mm, 40mm and 50mm sizes but they are actually larger than push-fit sizes and they are NOT interchangeable with push-fit, although compression fittings can be used on either type.

Summing Up :
Sorry to get so technical, but these are the facts I'm afraid.
So first and foremost you shouldn't buy or use this pipe unless you are going to use 'solvent welding'.
If your fitting are 'push fit' i.e. just push into a joint that has a rubber/silicone ring inside it you need a standard push-fit pipe for it, and you need to look elsewhere rather this this pipe.

And you thought plumbing was easy didn't you, and as you can see it isn't, I have been caught out more than once myself, on a new house it is fine but as I said if your house is 1979..ish or earlier you might have problems.
It can get even more complicated, but lets not go there for my sanity !

I do hope this has been of some help though ?

ASIN	B099ZPT36Y
Brand	generic
Colour	White
Country of Origin	United Kingdom
Customer Reviews	4.6 out of 5 stars 18 Reviews
Item Length	1 Metres
Item length	1 Metres
Manufacturer	Aigher
Material	Polyvinyl Chloride (PVC)
Nominal Wall Thickness	1
Nominal wall thickness	1
Outside Diameter	5E+1 Millimetres
Outside diameter	5E+1 Millimetres
Unit Count	1.0 Count

Solvent Weld Waste Pipe Fittings 32MM 40MM 50MM - Waste Pipe 1M Cut length - PVC (White, 50MM)

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