One of the most common sourcing mistakes in international fastener buying is mixing up standards. A “DIN 933 bolt” and an “ASME B18” hex bolt are not the same thing. This guide explains the three main fastener standard families — DIN, ISO and ANSI/ASME — so you can specify exactly what you need.
DIN (German / European, metric)
DIN standards originated in Germany and are widely used across Europe and Asia. They are metric (M6, M8, M10…). Common examples: DIN 933 (fully threaded hex bolt), DIN 931 (partially threaded hex bolt), DIN 934 (hex nut), DIN 125 (flat washer). Many factories still quote in DIN because buyers know these numbers well.
ISO (International, metric)
ISO is the global metric standard and is gradually replacing many DIN numbers. Equivalents include ISO 4017 (≈ DIN 933), ISO 4014 (≈ DIN 931) and ISO 4032 (≈ DIN 934). For most general bolts and nuts, DIN and ISO parts are interchangeable, but always confirm dimensions and property class.
ANSI / ASME (American, inch)
ANSI/ASME standards are used mainly in North America and use inch sizes (1/4″, 3/8″, 1/2″) with UNC/UNF threads. Key documents include ASME B18.2.1 (hex bolts and screws) and ASME B18.2.2 (nuts). Grades are marked SAE J429 (Grade 2, 5, 8) or ASTM (A307, A325, A193 B7).
Metric vs inch: the key takeaway
- Europe / Asia / most of the world: metric, DIN or ISO.
- USA / Canada: inch, ANSI/ASME with SAE/ASTM grades.
- Never assume an M8 equals 5/16″ — they are close but not interchangeable.
How to specify a fastener correctly
Give your supplier: (1) standard (e.g., DIN 933 / ISO 4017 / ASME B18), (2) size and length (M8×30), (3) property class or grade (8.8, 10.9, A2-70, Grade 5), (4) material and finish (carbon steel zinc plated, A4 stainless). The clearer the spec, the fewer surprises.
Source these fasteners from Chaoshuo Trading
Chaoshuo Trading is a China-based fastener source factory supplying bolts, nuts, screws, washers, rivets, threaded rods and custom fasteners in DIN/ISO standards, with factory-direct pricing and OEM customization. Contact us for a quote: info@chaoshuotrade.com | WhatsApp +86 158 0311 9164 | www.chaoshuotrade.com