BoltLabM12 Bolt Load Capacity
An M12 bolt's tensile load capacity depends on its thread pitch (coarse M12×1.75 or fine M12×1.25), its property class, and a safety factor you choose — there is no single "M12 capacity" figure that applies to every part sold as M12.
Use the Bolt Load Capacity Calculator to enter your own size, class, and safety factor; this page walks through how those inputs combine specifically for M12.
M12 thread geometry
M12 is offered in a coarse and a fine pitch, both supported by BoltLab's calculator:
| Designation | Nominal diameter | Pitch | Series |
|---|---|---|---|
| M12 × 1.75 | 12 mm | 1.75 mm | Coarse |
| M12 × 1.25 | 12 mm | 1.25 mm | Fine |
M12 × 1.75 coarse is the more commonly stocked pitch. The fine M12 × 1.25 option removes less material at the thread root, which shows up directly as a larger computed tensile stress area below.
M12 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 its sourcing.
Property classes supported for M12
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All source-verified ISO metric classes in BoltLab's dataset cover the 12 mm diameter, including the standard (≤M16) range of class 8.8. See fastener property classes for sourcing and which classes are currently held back.
Example M12 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. These figures are computed by the same formula and data code the calculator itself runs, so this table and the tool can never disagree.
The role of safety factor for M12
The proof-based figure above describes the fastener before any margin is applied — dividing by an appropriate safety factor accounts for load uncertainty, manufacturing tolerance, and the consequences of failure in your specific application. BoltLab does not suggest a default safety factor for M12 or any other size; see Bolt Load Capacity Basics for why no single value applies universally across applications and design codes.
Practical interpretation
M12 is a larger general-purpose and structural metric size, often specified where M8 or M10 would not provide enough margin for the application. As with every size, the property class stamped on the bolt head — not the diameter alone — drives most of the real difference in capacity: an M12 class 4.6 bolt and an M12 class 12.9 bolt share the same tensile stress area but differ in proof-based capacity by more than 4×. Always confirm the class from the actual head marking (see Bolt Head Markings) rather than assuming it from size or supplier description.
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.