5/16"-18 x 5/8" Zinc Finish ASTM A307 Grade A Round Head Carriage Bolt / THREAD CLASS: 2A THREAD DIRECTION: RIGHT-HAND FASTENER LENGTH: 0.625 INCHES NOMINAL HEAD STYLE: C37 ROUND HEAD DIAMETER: 0.688 INCHES MINIMUM AND 0.719 INCHES MAXIMUM HEAD HEIGHT: 0.156 INCHES MINIMUM AND 0.176 INCHES MAXIMUM END ITEM IDENTIFICATION: 4120014490459 NOMINAL THREAD DIAMETER: 0.313 INCHES THREAD QUANTITY PER INCH: 18 SPECIAL FEATURES: FASTENER HAS A SQUARE NECK BETWEEN HEAD AND THREADS MATERIAL: STEEL OVERALL SURFACE TREATMENT: ZINC OVERALL THREAD SERIES DESIGNATOR: UNC