Which standard defines dimensions for bolts, nuts, and washers?

The organization that is responsible for addressing dimensional guidelines and tolerances for fasteners is the American Society of Mechanical Engineers (ASME). This organization was founded in 1880 and now has over 130,000 members in 151 countries. In addition to being a standards organization, ASME is also involved in research and development, training and professional development, conferences and publications, and government relations.

Here are the ASME dimensional standards for common construction fasteners:

ASME B18.2.1 Hex bolts, heavy hex bolts, square head bolts This specification covers head height, width across the flats, width across the corners, and several other dimensions.
ASME B18.5 Carriage bolts, round head bolts, countersunk bolts This specification covers head height, head diameter, size of the square neck of carriage bolts, countersunk head angle, and several other dimensions.
ASME B18.2.2 Hex nuts, heavy hex nuts, square nuts, hex jam nuts, heavy hex jam nuts, hex coupling nuts, lock nuts Nut height, width across the corners, and width across the flats of the nut are the three primary dimensions specified under this standard.
ASME B18.2.6 Structural bolts This standard outlines head dimensions and other measurements for heavy hex structural bolts.
ASME B18.21.1 Standard flat washers, lock washers This washer standard includes dimensions for thickness, inside diameter, and outside diameter.

Portland Bolt manufactures fasteners with head dimensions that comply with these standards. We will also automatically provide submittal drawings which states our fasteners will meet the ASME standards. If you have any questions about ASME standards or anything else, feel free to contact our team and we will be more than happy to assist.

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