Take a 15mm straight coupler, e.g.
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts ˆ231&id921
The internal diameter if the fitting is obviously 15mm, to take naturally 15mm pipe. But what is the thread size on either end?
Now take something like:
http://www.screwfix.com/app/sfd/cat/pro.jsp?id 341&ts907
This is described as Female Iron Coupler Compression Fittings 15mm×½"
The 15mm must relate to the internal diameter and I guess the thread size is the same on one end as the stright coupler. But what does the 1/2" relate to? The internal diameter on the other end or the thread size?
Help!
Graham