Bath waste measurement question

joho

Lovely DIY peeps - we need to replace our pop-up bath waste and overflow. Can anyone tell me which part the 'standard' fitting size 1.5" measurement applies to?

The visible metal rim of the existing waste outlet is 70mm, and the actual visible opening (where the water disappears) is 1.75". 

Yes, I know - mixed measurements. But everything I see online has mixed measurements. Just to help obviously!

Thank you.x

Rodders53

1.5 inches ( G 1 1/2 ) refers to the waste pipe and trap thread on the very bottom of the bath waste to suit 40mm waste pipework.

The hole(s) for waste and overflow are a different size.
44mm and 52mm are common size for the overflow hole: 
44mm is almost 1 3/4 inch (1.732 in fact) and 52 is a bit over 2 inches.
44mm is invariably used for the waste exit hole. 

https://www.qssupplies.co.uk/bathroom-furniture-shower-taps/300251.htm

joho

Thank you @Rodders53