Method
Density. The standard density of the material selected — carbon and alloy steel, austenitic stainless, duplex, brass, aluminium or titanium — applied to the computed volume.
Threaded length. A cylinder on the pitch diameter d₂ (ISO 724: d − 0.6495·P; UN: D − 0.6495/n). A rolled thread has the mass of its blank, and the pitch diameter is that blank to within 1%.
Unthreaded shank. A cylinder on the nominal diameter. Thread length b per ISO 4014 / DIN 931 (2d + 6 up to 125 mm, 2d + 12 to 200, 2d + 25 above), per ASME B18.2.1 (2D + ¼″ up to 6″), and per ASTM F3125 for structural bolts.
Hex heads and nuts. A hexagonal prism on across-flats s: volume 0.866·s²·k. Bolt heads carry a 5% deduction for the top chamfer and washer face; metric nuts 3% for their two chamfers, heavy hex nuts 5% for their double chamfer to the across-flats circle, less the bore on d₂. Spring washers lose 5% for the split gap. Across-flats and heights taken from ISO 4014/4017, DIN 931/933, ISO 4032, DIN 934, ASME B18.2.1 (hex and heavy hex), ASTM A194 (heavy hex nuts) as selected.
Socket heads. Cylinder d_k × k less the hexagon socket to its depth, ISO 4762 / DIN 912. Countersunk heads as a 90° cone frustum less the socket, ISO 10642 / DIN 7991.
Washers. Flat: annulus on d₁, d₂, s from ISO 7089 / DIN 125A, DIN 9021, ASTM F436. Spring: a square-section ring, DIN 127 B.
Bent bolts. Developed length along the centreline including the bend arc at radius R + d/2, on the nominal diameter; plates as prisms less the hole.
Coating. Hot-dip galvanizing adds the zinc layer over the computed surface area at the selected thickness — about 2% on M12, under 1% above M30.
Accuracy. ±3% against a weighed batch for hex products; ±5% for socket, countersunk and lock nuts where head detail varies more between makers. Not a certified weight.
