There are a variety of copper tubing sizes used on espresso machines. They have all their own application. Seen you don’t require a 12mm tube for a pressure switch for instance, this does save money.
The smallest sizes of copper tubing on espresso machines is the copper tubing for the pressure gauges. These have a outer diameter of 4mm and a wall thickness of 1mm. They can be used with a 4mm brass welding cap.
The copper tubing size of 6mm is one of the smaller size diameters. This specific type of tubing is used to connect pressure switches. The tubing itself has a outer diameter of 6mm and a wall thickness of 1mm. For this tubing size you have various sizes of welding end caps, such as the 6mm welding end cap 3/8” fitting
The 8mm tubing sizes is the middle size of the sizes used on coffee machines. This size can be used on domestic espresso machines as a steam tube or a filling valve tube. You can use various types of welding caps for this application such as the Welding end cap 8mm 3/8”. This specific tube has a outer diameter of 8mm and a wall thickness of 1mm.
This is one of the biggest sizes of copper tubing. These can be used on commercial espresso machines for instance on water inlet systems. They can be used in combination with a welding cap 10mm. For this tube you have a outer diameter of 10mm and a wall thickness of 1mm.
This is the biggest size of copper tubing used on espresso machines. You will find this type of tubing used on for instance the tubing which goes towards the brewing group of the espresso machine. The outer diameter is 12mm and the wall thickness is 1mm.