Metric Thread Size Guide: M3 to M64 — Pitch, Strength & Selection
A practical guide to metric thread sizes from M3 to M64: standard pitches, diameter-strength relationships, and how to pick the right thread size for your application.
How metric thread sizes work
A metric fastener is designated by nominal diameter and pitch in millimeters — for example, M8 x 1.25 means an 8 mm diameter with 1.25 mm thread pitch. When pitch is omitted (e.g., M8), the coarse pitch is assumed: 1.25 mm for M8, 1.5 mm for M10, and so on.
Common sizes and coarse pitches
The most common metric sizes: M3 (0.5), M4 (0.7), M5 (0.8), M6 (1.0), M8 (1.25), M10 (1.5), M12 (1.75), M16 (2.0), M20 (2.5), M24 (3.0), M30 (3.5), M36 (4.0), M42 (4.5), M48 (5.0), M56 (5.5), M64 (6.0). Coarse threads are the default for general use — they assemble faster, resist cross-threading, and are more tolerant of dirt and damage.
Fine vs coarse threads
Fine threads (e.g., M10 x 1.25 instead of M10 x 1.5) have a smaller pitch. They provide higher tensile strength for the same diameter, better vibration resistance, and finer adjustment — which is why they are used in automotive engines and precision equipment. The trade-offs: higher cost, easier to cross-thread, and faster wear in dirty environments.
Strength by grade
Metric property classes tell you the tensile strength: 4.8 (400 MPa), 8.8 (800 MPa), 10.9 (1000 MPa), 12.9 (1200 MPa). The first digit is ultimate strength in hundreds of MPa; the second is the yield ratio. For structural connections, 8.8 is the common minimum; 10.9 and 12.9 are for high-load bolting.
Choosing the right diameter
As a rule of thumb: M3-M5 for electronics and small assemblies, M6-M10 for furniture, machinery guards and light structural, M12-M20 for structural steel and heavy equipment, M24+ for large flanges and high-capacity connections. When in doubt, match the thread to the load — oversized bolts on thin sections invite stripping of the threaded hole.
Materials and finishes by size
Small diameters (M3-M8) are typically stainless or zinc-plated carbon steel. Larger structural sizes (M12-M24) are usually high-strength alloy steel (8.8-10.9) with hot-dip galvanizing or Dacromet. Taily Metal supplies the full range M3-M64 in carbon steel, stainless, alloy steel, brass and aluminum.
Need a specific size or custom thread?
Non-standard pitches, left-hand threads, and custom lengths are all buildable. Send your specification to [email protected] — our engineers will confirm the best production route and quote within one working day.
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