Question 1: What are the marks shown on the head of a bolt?
Usually fastener standards specify two types of marks to be on the head of a bolt. The manufacturer's mark is a symbol identifying the manufacturer (or importer). This is the organisation that accepts the responsibility that the fastener meets specified requirements. The grade mark is a standardised mark that identifies the material properties that the fastener meets. For example 307A on a bolt head indicates that the fastener properties conform to the ASTM A307 Grade A standard.