Final answer:
In welding, a square symbol is used to represent a consumable insert, which is a preformed piece of filler metal that ensures complete joint penetration and quality in the weld.
Step-by-step explanation:
In welding symbols, a square symbol specifies a consumable insert. This is part of the symbolic language used in welding blueprints and detailed drawings to communicate how a particular weld should be performed. A consumable insert is a preformed piece of filler metal that is placed in the root of the joint and consumed completely during the welding process to become part of the weld. It is used in certain types of joints where achieving complete joint penetration and optimizing quality are critical.