Metric fasteners follow a consistent naming system that tells you everything you need to know about the bolt, nut, or threaded rod you're working with. Once you understand the system, specifying and ordering the right fastener becomes straightforward. Here's a quick guide.
The M number — thread diameter
The "M" prefix stands for metric, and the number after it is the nominal thread diameter in millimetres. So M10 means the threaded portion of the bolt or rod is 10mm in diameter.
Common sizes you'll encounter: M6, M8, M10, M12, M16, M20, M24. Larger sizes like M30 are used in heavy structural work.
Length
For bolts and set screws, the length is given after the diameter — for example, M10x50mm means a 10mm diameter bolt with a 50mm shank length. For threaded rods and studs, the full length is specified (e.g. 1 metre).
Thread pitch
Metric threads come in coarse or fine pitch. Unless otherwise specified, most structural fasteners use coarse pitch (the standard). For M10, the coarse pitch is 1.5mm. Fine pitch (e.g. 1.25mm) is mainly used in precision engineering and automotive applications.
Grade — tensile strength
The grade tells you how strong the fastener is. Common grades:
- Grade 4.8 — standard mild steel, used for general applications where loads are moderate
- Grade 8.8 — high tensile steel, used for structural bolting and load-bearing connections
- Grade 10.9 — very high tensile, used in automotive and high-load engineering
Finish — BZP, HDG, A4
The finish affects corrosion resistance. The most common options are Bright Zinc Plated (BZP) for internal use, Hot Dip Galvanised (HDG) for outdoor structural use, and A4 stainless steel for marine and corrosive environments. For a full breakdown, read our guide: BZP, HDG, or Stainless Steel?
DIN standards
You'll often see a DIN number alongside a fastener specification — this is a German engineering standard that defines the dimensions and tolerances precisely. Common ones: DIN 933 (hex head set screws), DIN 934 (hex nuts), DIN 976 (threaded rod). Our products are manufactured to DIN specification throughout.
Finding the right fastener
Browse our full range of threaded rods, nuts, hex head set screws, and washers — all in metric sizes, with fast UK dispatch and free delivery over £60.
