BoltLabM8 Bolt Load Capacity
An M8 bolt's tensile load capacity depends on which thread pitch (coarse M8×1.25 or fine M8×1.0), which property class it's made to, and the safety factor applied — there is no single "M8 capacity" number.
Use the Bolt Load Capacity Calculator with your own size, class, and safety factor for an exact estimate; this page shows how the inputs combine for M8 specifically.
M8 thread geometry
M8 is available in a coarse and a fine thread pitch, both supported by BoltLab's calculator:
| Designation | Nominal diameter | Pitch | Series |
|---|---|---|---|
| M8 × 1.25 | 8 mm | 1.25 mm | Coarse |
| M8 × 1.0 | 8 mm | 1.0 mm | Fine |
A finer pitch removes slightly less material from the thread root, which is why M8×1.0 computes a marginally larger tensile stress area than M8×1.25 despite sharing the same nominal diameter.
M8 tensile stress area
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Computed live using At = 0.7854 × (D − 0.938194 × P)² — see tensile stress area for the full formula derivation and why it's smaller than the area implied by nominal diameter alone.
Property classes supported for M8
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All source-verified ISO metric classes in BoltLab's dataset cover the 8 mm diameter. See fastener property classes for how these values are sourced and which classes are held back.
Example M8 capacity calculations
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Each row uses a safety factor of 4, shown for illustration only — substitute the factor appropriate to your application in the calculator. Every number here is computed by the same formula and data code the calculator runs, so it cannot drift from the tool's own output.
The role of safety factor for M8
The proof-based capacity above is a starting point, not a working limit — dividing it by an appropriate safety factor accounts for manufacturing tolerance, load uncertainty, and the consequences of failure in your specific application. BoltLab does not suggest a default safety factor for M8 or any other size; see Bolt Load Capacity Basics for why no single value applies universally.
Practical interpretation
M8 sits in the middle of the commonly stocked metric fastener range, used across general machinery, automotive, and fixture applications. The number that matters for a real design is never "what can an M8 hold" in the abstract — it's the specific thread pitch, the specific property class actually marked on the fastener's head, and a safety factor chosen for that job. Two M8 bolts that look identical can differ in tensile capacity by more than 3× depending on whether they're class 4.6 or class 12.9, which is why reading the head marking (see Bolt Head Markings) before relying on any capacity figure matters.
Limitations
This page and the calculator behind it estimate fastener tensile capacity only — not shear, joint, thread-stripping, nut, connected-material, fatigue, or preload behavior. See the calculator's own limitations section for the complete list, and verify safety-critical work with a qualified engineer and the applicable design code.