ANSI & ASTM Standard Parts — A307, A325, A193

Standard overview

The American fastener system runs on two layers that are easy to confuse because both appear on the same drawing. The ASME B18 series defines dimensions and geometry: head shape, across-flats, thread, length tolerance. The ASTM lettered specifications define material, strength and marking: what steel, how strong, what to stamp on the head. Neither does the other’s job. A drawing that says only “A325 bolt” names the material and strength but not the geometry; one that says only “B18.2.1 bolt” names the geometry but not the strength. A real part needs one of each, and mixing the two layers is the fastest route to a wrong part — a supplier can meet the dimensional standard in the wrong material, or the material standard in the wrong geometry, and still point at a compliant callout.

A complete callout pairs them. The pattern in the table note — ASME B18.2.1 dimensions in ASTM A325 material — is how every structural bolt we make is specified: B18.2.1 fixes the hex head and shank geometry, A325 fixes the quenched-and-tempered material, the 120 ksi tensile requirement (105 ksi over 1 in), and the head marking. The thread is a third, usually implied, document: ASME B1.1 for UNC, UNF and UNEF. The dimensional standard and the material standard are orthogonal — change the material and the dimensions stay put, change the dimensions and the strength is untouched.

Sizes, threads and grades we cover

The table on this page lists which ASME or ASTM document covers which part, 32 rows split into two halves: the B18 rows describe parts, the ASTM rows describe what they are made of and how strong they are.

The structural bolting family is where most quoting confusion lives, because it has just been reorganised. For decades a structural bolt was either an A325 — quenched and tempered, 120 ksi up to 1 in and 105 ksi above — or an A490, an alloy-steel bolt at 150 ksi. The two looked alike, were not interchangeable, and the head marking carried the difference. Both, together with the tension-control grades, have now been folded into a single document, ASTM F3125, which re-labels them as grades of one specification rather than separate standards. Older drawings still say A325 or A490, and we quote to the drawing as written; a new project should call out F3125 and name the grade.

Outside structural work we cover the full ladder: A307 general-purpose carbon bolts at 60 ksi, A354 quenched-and-tempered alloy bolts in Grades BC and BD, A449 general quenched-and-tempered bolts, A193 alloy and stainless bolting for high-temperature service with its matching A194 nuts, and SAE J429 for the Grade 2, 5 and 8 hex cap screws used across machinery. Threads follow ASME B1.1 for UNC, UNF and UNEF, and the inch fasteners page carries the threads-per-inch tables.

Materials and finishes

Two families sit at the edge of what people call fasteners and get cited by ASTM alone. Anchor bolts are specified by ASTM F1554 in three yield grades — 36, 55 and 105 ksi — for straight, bent (hooked) and headed configurations; the grade is the material, and the geometry is usually drawn rather than standardised. Driven fasteners — nails, spikes and staples — fall under ASTM F1667, where the specification covers the shank, point and head that are driven into the substrate rather than threaded into it.

Material follows the specification’s grade. The common choices in our workflow are aluminium 2024, 5052, 6061 or 7075; stainless 301, 303, 304, 304L, 316, 316L or 17-4PH; carbon steel 1045 or 1215; alloy and tool steel 4140, D2 or O1; and brass, bronze, copper or titanium, with finishes — zinc or nickel plating, black oxide, passivation, anodising — applied through our vetted partner network under one quality process. The materials and surface finishes pages list the options, and custom bolts and custom nuts show the same two-layer callout applied to machined parts.

Ordering notes

Quoting a part that cites two standards at once is mostly a matter of collecting both halves and checking that they agree. We need the dimensional standard (the ASME B18 number that fixes geometry), the material standard (the ASTM letter that fixes strength and marking), the diameter and length, the thread series and pitch, any coating, and the quantity. A callout such as “ASME B18.2.1, ASTM A325, 3/4-10 × 2-1/2, hot-dip galvanised” is complete enough to quote on the spot; a callout that names only one of the two leaves a question we ask before we price.

Send the drawing or the callout line through the quote page and we return a price with DFM feedback within 24 hours. Where an older designation has been folded into F3125 or replaced, we flag the mapping and quote to the current document unless you direct otherwise.

Tolerances default to ISO 2768-m general tolerance and ±0.01 mm where the drawing demands it — the tolerances page explains each level — and we produce from 1 piece for samples and from 50 pieces for production runs, shipping with a material certificate (MTR) and pre-shipment photos.