I am replacing old 1-3/4” diameter hex bolts that are marked with 3 radial lines. What grade are these bolts?
The SAE J429 Grade 5 specification used to share the same head marking requirement as ASTM A449. A449 and Grade 5 are virtually identical both chemically and mechanically, but where the Grade 5 specification stops at 1-1/2” diameter, A449 continues up to 3”. They shared the three radial line head marking that Grade 5 still has today up until 2006 when A449 received its own “A449” stamping requirement. Therefore, since Grade 5 bolts don’t exist in 1-3/4” diameter, you will replace the bolts in question with ASTM A449.