The ASTM A563 specification covers the chemical and mechanical requirements for carbon and alloy steel nuts used on bolts, studs, and externally threaded fasteners. The charts below address over tapping allowances for hot-dip galvanized nuts, grade marking requirements, and mechanical requirements.
According to the A563 specification, “The requirements for any grade of nut may, at the supplier’s option, and with notice to the purchaser, be fulfilled by furnishing nuts of one of the stronger grades specified herein unless such a substitution is barred in the inquiry and purchase order”. This is important because some nut grades are not readily available in certain sizes and finishes. Additionally, the specification allows for the substitution of ASTM A194 grade 2H nuts in lieu of A563 grade DH nuts due to the lack of availability of
grade DH nuts in nominal sizes 3/4″ and larger.

Grades in ASTM A563 :
A : Carbon Steel Hex and Heavy Hex
B : Carbon steel, hex or heavy hex
C : Carbon steel, quenched and tempered, heavy hex
D : Carbon steel, quenched and tempered, heavy hex
DH : Carbon steel, quenched and tempered, heavy hex
C3 : Weathering steel, quenched and tempered, heavy hex
DH3 : Weathering steel, quenched and tempered, heavy hex

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