Mean Wall Thickness
For a tube this is the sum of four wall thickness measurements, made at 90o intervals around the diameter, divided by four.
Melt, Cast, Heat
These terms are used interchangeably to refer to the product of a single melting furnace charge. Sometimes the furnace contents are tapped into two or more ladles when the product of each ladle may be called a separate cast. It is always assumed that the chemical composition of an entire cast will be uniform. This is described as the “cast analysis” on a Certificate of Conformity etc.
An extrusion die, with more than one hole, allowing multiple extrusions to be made simultaneously from one billet.