M8 x 1.25 12.9 (Metric thread)
The M8 x 1.25 12.9 is a ISO metric threaded fastener with a 1.25 mm thread pitch. It develops a maximum recommended assembly torque of 40 Nm dry, a single-shear capacity of 27.3 kN, and a minimum tensile strength of 1220 MPa. It is manufactured from quenched-and-tempered alloy steel with high strength and a black-oxide or zinc finish.
Fastener Specifications
| Specification | Value |
|---|---|
| Thread System | Metric |
| Designation | M8 x 1.25 |
| Thread Pitch | 1.25 mm |
| Property Class / Grade | 12.9 |
| Material | Alloy Steel |
| Tensile Strength | 1220 MPa |
| Max Assembly Torque | 40 Nm |
| Shear Strength (single) | 27.3 kN |
Thread & Grade Notes
M8 x 1.25 is a Metric thread. 12.9 fasteners are a high-strength grade with a minimum tensile strength of 1220 MPa. Thread pitch of 1.25 mm determines how many turns are required to engage a given length and how resistant the joint is to loosening through vibration.
- Preload: torque to roughly 65–70% of proof load (≈ 40 Nm dry).
- Shear joints: a single bolt in shear carries about 27.3 kN before failure; use multiple fasteners or larger sizes for higher loads.
- Corrosion: matching fastener and structure materials avoids galvanic corrosion, especially with stainless in chloride environments.
Tightening & Substitution Notes
Always torque to the value specified by the joint engineer; the 40 Nm figure here is a generic dry assembly target. When substituting, match the thread system (Metric), pitch (1.25 mm), grade (12.9), and at minimum the shear capacity (27.3 kN). A lower-grade fastener in the same size reduces both preload and shear capacity; stainless grades trade some strength for corrosion resistance and are prone to galling.
Frequently Asked Questions
What is the thread pitch of the M8 x 1.25?
1.25 mm.
How much torque does an M8 x 1.25 12.9 bolt take?
Approximately 40 Nm dry assembly torque.
What is the shear strength of the M8 x 1.25 12.9?
About 27.3 kN in single shear.
What is the tensile strength of the M8 x 1.25 12.9?
1220 MPa minimum.
What material is the M8 x 1.25 12.9?
Alloy Steel.