Tyr is the Norse god of law, justice and the assembly, who put his hand in the wolf Fenrir's mouth as surety for a binding that could not hold him. When the wolf was bound, the hand was lost. He is the god who pays the price of the rule he upholds.
Modern Practice
Tyr is called on before oaths, contracts, court and any assembly that has to decide fairly. His day is Tuesday, and his practice is to name the cost of the promise before making it.