Hi All Thanks for the comments. It seems that most boiler makers use SAE660 and provided you dont overheat it then it's fine. If you overheat it then the lead rises to the surface and it's time to give up!! Andy MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.