Underground water pipe sizes

[SandyMac]

I've done alot of on-farm plumbing with blue 20mm and 25mm water pipe and plasson fittings. I need to join some blue to some old black poly. I think I'm right in saying that blue is measured externally, but the older imperial black is measured internally, in which case it is 3/4". Can I use a 25mm plasson compression fitting on the black, or will I need to get a metric to imperial connector? I think the Philmac ones do both??, but I can't seem to get on so well with them. Any advice gratefully received.

 

[stevetheplumber]

philmac have various rubbers for all combinations just ask at the merchants

 

[justlead1]

Hi Plasson do a range of fitting for your needs. Cut a bit of and take it to the merchants so as to match both inserts and external diameter required.