M8 x 1.25 8.8 (Metric thread)
The M8 x 1.25 8.8 is a ISO metric threaded fastener with a 1.25 mm thread pitch. It develops a maximum recommended assembly torque of 24 Nm dry, a single-shear capacity of 17.6 kN, and a minimum tensile strength of 800 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 | 8.8 |
| Material | Alloy Steel |
| Tensile Strength | 800 MPa |
| Max Assembly Torque | 24 Nm |
| Shear Strength (single) | 17.6 kN |
Thread & Grade Notes
M8 x 1.25 is a Metric thread. 8.8 fasteners are a high-strength grade with a minimum tensile strength of 800 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 (≈ 24 Nm dry).
- Shear joints: a single bolt in shear carries about 17.6 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 24 Nm figure here is a generic dry assembly target. When substituting, match the thread system (Metric), pitch (1.25 mm), grade (8.8), and at minimum the shear capacity (17.6 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 8.8 bolt take?
Approximately 24 Nm dry assembly torque.
What is the shear strength of the M8 x 1.25 8.8?
About 17.6 kN in single shear.
What is the tensile strength of the M8 x 1.25 8.8?
800 MPa minimum.
What material is the M8 x 1.25 8.8?
Alloy Steel.