I promised to measure the copper pipes I have in my home, done with a micrometer at 20 C.
3/4" pipe is 22,2 mm OD. 19,9 mm ID. 1/2" pipe is 16,0 mm OD. 13,8 mm ID. 1/4" pipe is 9,7 mm OD. 7,9 mm ID. Seems like the wall thickness on this pipe is very close to 1 mm. None of the inch sizes have any correlation to the actual "nominal" size. Allowing for manufacturing tolerances, these pipes are as near to whole millimeter sizes as is possible. When you go into a hardware store and try to find fitting that are labeled 1/2"or 3/4", etc. The actual size bears no relationship to actual size which can be very frustrating if you measured something at home and expect this to match what they have in the store. A 3/4" fitting from one manufacturer will fit the 1/2" fitting from another manufacturer, so each company is choosing any definition they want for the named size. Mike Payne
