A structural bolt grade, listed within ASTM F3125, used to connect steel beams, columns and bracing. It is a heavy hex bolt of quenched and tempered medium-carbon steel, installed with a heavy hex nut, plus hardened washers where the connection calls for them, and pretensioned by turn-of-nut, direct tension indicators or twist-off control. Its stronger sibling A490 reaches 150 ksi but is not galvanized because of embrittlement risk.
Connection calls for seven-eighths A325 slip-critical, so every bolt gets turn-of-nut and the inspector watches the match marks.
Ironworkers read the head: A325 for the common bolt, A490 for the hard one, and a line under the grade marks weathering steel.
Also heard as
- A325 bolt
- F3125 Grade A325
Related terms
Heavy hex
A hex head or nut wider across the flats than the regular series, used for structural and pressure bolting.
Turn-of-nut
A pretensioning method that snugs the nut, match-marks it, then turns it a fixed fraction of a turn.
DTI
Direct tension indicator: a hardened washer with bumps that flatten when the bolt reaches required tension.
TC bolt
Tension control bolt: a structural bolt with a splined tip that shears off once the right tension is reached.
HDG
Hot-dip galvanized: coated by dipping in molten zinc, leaving a thick, rugged layer for outdoor steel.