Metric Fasteners & Metric Machined Parts — DIN 912, 933, 934

Standard overview

A metric fastener is identified by its nominal major diameter in millimetres followed by the thread pitch. A part called out as M10 × 1.5 is an external thread with a nominal major diameter of 10 mm and a pitch of 1.5 mm. When the pitch is omitted — M10 on its own — the coarse series is assumed, because every metric diameter has one designated coarse pitch and a choice of finer ones. The profile is a 60° V-thread defined by the ISO metric thread system, and common machined parts such as socket head cap screws, hexagon bolts and hexagon nuts are referenced to DIN 912, DIN 933 and DIN 934.

Buyers working to metric drawings usually face two practical questions at the start: which pitch to order, and which property class the part must carry. This page walks through both, along with how the hex size is chosen and how to put a metric thread on a drawing so there is nothing left to guess. The thread size and pitch tables rendered on this page are our working reference; they list the coarse and fine pitch for each diameter we machine, and the fraction-to-millimetre chart that helps when a legacy drawing mixes the two systems.

Sizes, threads and grades we cover

Coarse pitch is the default for most general assembly. The thread is deeper relative to its length, it taps and threads faster, and it tolerates a little surface damage or a slightly oversized pilot hole better than a fine thread. Choose coarse unless there is a reason not to. Fine pitch has a shallower helix angle and more engaged threads over the same length, so it resists loosening under vibration better, allows finer axial adjustment, and leaves more wall thickness when the thread is cut into a thin section. The trade-off is that a fine thread cross-threads more easily and is easier to damage during handling.

One point that surprises engineers is that the width across flats does not scale with the diameter. A hexagon is sized so a full range of fasteners can be driven with the same small set of wrenches, and so the head has enough bearing area and strength for the load. The result is a stepwise series — an M10 hexagon is 16 mm or 17 mm across flats depending on the standard, an M12 is 18 mm or 19 mm — rather than a continuous curve. If a socket, wrench or spanner size matters to your assembly, put it on the drawing.

Property class is the metric strength grade. For steel bolts the common classes are 8.8, 10.9 and 12.9; the first number is the minimum tensile strength in hundreds of megapascals and the second is the yield-to-tensile ratio. Stainless parts use the A2 and A4 designations of ISO 3506. The thread size and pitch table above lists the coarse and fine pitch for each diameter; the property class and any head marking should be called out separately.

Materials and finishes

Metric fasteners can be produced from the full range of materials we machine. Aluminium 2024, 5052, 6061 and 7075 suit low-weight, corrosion-sensitive assemblies; 7075 is the choice when strength matters, and 2024 when the part also has to hold a fine thread under load. Stainless steel 301, 303, 304, 316, 316L and 17-4PH cover most corrosive environments, with 303 easiest to machine, 316L best where chlorides are present, and 17-4PH the grade to specify when the fastener needs both corrosion resistance and high strength. Carbon steel 1045 and 1215 are economical for general hardware, and alloy steel 4140 is the material to specify when the part will be heat-treated to a high strength class. Brass, copper, bronze and titanium are available for conductive, decorative and high-strength-to-weight applications. The materials page lists the grades and the process each one runs on.

Finish follows the same pattern as every other secondary process on a machined part: plating, black oxide, anodising and heat treatment are all available, produced in-house or through our vetted partner network and managed under one quality process so the result is consistent from one batch to the next. Zinc plating is the most common protective finish for steel hardware; aluminium parts are typically anodised; stainless can be supplied bright or passivated. Tell us the finish by name and, where it matters, the coating thickness, and we will match it. See our custom bolts, custom nuts and custom screws pages for how these materials are machined into finished parts.

Ordering notes

Specifying a metric part on a drawing is easiest when the following appear together: nominal size and pitch (for example M8 × 1.25), the thread tolerance class (6g for external threads, 6H for internal), the property class or material grade, the head style and drive type, the length, the material, and the finish. Leaving any one of these off forces a guess, and the guess is where cost and lead time are usually lost. If you are replacing an off-the-shelf part, naming the DIN or ISO reference — DIN 912, DIN 933, DIN 934 — removes the remaining ambiguity.

Send the drawing through the request-a-quote form and you will get pricing within 24 hours with DFM feedback: we flag thread features that will be difficult to machine, suggest a different pitch or grade where it saves money, and confirm the material and finish before anything is cut. Orders start at 50 pieces, samples from a single piece, with samples in 5–10 days and production in 25–35 days after sample approval. A non-standard pitch or an unusual across-flats size is handled the same way as any other machined feature — see our drawing requirements and tolerances pages for what to put on the print.