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Fastener knowledge
Plain-English guides from 51 years in fasteners: how bolts are made, which steel goes into which grade, how they are hardened, coated and tested.
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From wire rod to finished bolt
Read in order for the full story, or jump to the topic you need.
Manufacturing
How a bolt is made: from steel wire rod to finished fastener
The full fastener manufacturing process step by step: wire rod, annealing, drawing, cold heading, thread rolling, heat treatment, coating and inspection.
Grades
Bolt grades explained: 4.6 to 12.9, strength, hardness and the steel behind each
What 8.8, 10.9 and 12.9 mean: tensile and yield strength, hardness, elongation, matching nut classes, ASTM and SAE equivalents, and which raw material and heat treatment each grade uses.
Grades
Stainless steel fastener grades: A2, A4 and beyond, with chemistry and properties
ISO 3506 stainless fastener grades A1 to A8, duplex D2 to D8, martensitic and ferritic: chemical composition, property classes 50 to 100, tensile and proof strength, matching AISI grades and how they are made.
Grades
ASTM fasteners explained: A193 B7, A194 2H, A320, A325, A490 and more
Complete guide to ASTM bolting: raw materials, manufacturing process, heat treatment, chemical composition and mechanical properties of A193, A194, A320, F3125 (A325, A490), A307, A449, A354, A563, F436 and F1554.
Raw materials
Fastener raw materials: which steel goes into which bolt
Carbon, boron, alloy and stainless steels for fasteners: ISO 898-1 chemistry limits, typical wire rod grades for 4.6 to 12.9, A2 and A4 stainless, brass, aluminium and titanium.
Manufacturing
Heat treatment of fasteners: annealing, hardening and tempering
Why high-tensile bolts are quenched and tempered, the 425 °C minimum tempering rule in ISO 898-1, case hardening of self-tapping screws, and why stainless is not heat treated.
Grades
Fastener heat treatment temperature chart: annealing, hardening, tempering and more
Typical temperatures for spheroidise annealing, hardening, quenching and tempering of fastener steels (10B21, C35/C45, 42CrMo4), minimum tempering rules for 8.8 to 12.9 and ASTM grades, baking, galvanising and zinc flake curing.
Manufacturing
Cold heading vs hot forging, and rolled vs cut threads
How fastener heads and threads are formed: cold heading on multi-station formers, hot forging of large bolts, and why rolled threads beat cut threads.
Finishes
Fastener coatings and finishes, and the hydrogen embrittlement risk
Zinc plating, hot-dip galvanising, zinc flake, phosphate and black oxide compared: thickness, salt spray life, thread fit and hydrogen embrittlement risk for 10.9 and 12.9.
Manufacturing
How nuts, washers and rivets are made
Nut forming and tapping, oversize tapping for galvanised nuts, nylon-insert and all-metal lock nuts, washer stamping, spring washers, wedge-lock washers and blind rivets.
Quality
How fasteners are tested: quality checks from steel to shipment
Fastener tests explained: tensile, proof load, wedge, hardness, decarburisation, impact, thread gauges, coating thickness and salt spray, plus head markings and inspection certificates.