Engineering
Engineering calculators
Three tools that compute from published standard formulas — the ISO 898-1 stress area, the ISO 261 coarse pitch series and the conventional tap-drill rule. No company data, no magic numbers: every output can be reproduced by hand.
Tool one
Preload and illustrative torque
Pick a size and property class. The stress area comes from the ISO 898-1 formula, preload from a stated fraction of the proof load, and torque from T = K·F·d at the nut factor you enter.
Stress area As
2.073 mm²
As = π/4 × (d − 0.9382 P)²
Target preload
929 N
70% × 640 MPa × As
Illustrative torque
0.372 N·m
T = K · F · d at your K
Tap drill (d − P)
1.60 mm
≈75% thread in steel
The torque figure is a worked example, not a specification. K varies with finish, coating, washer face and speed — an error in K becomes an error in preload of similar proportion. Establish the assembly torque on your joint, with your insert and your driver.
Tool two
Reference table, M0.6 – M6
The same calculation as a table, so you can check the tool against the printed values. Stress areas are pure geometry; the load and torque columns assume class 8.8, a 70% preload fraction and K = 0.20.
| Size | Coarse pitch (mm) | Stress area As (mm²) | 70% proof load, class 8.8 (kN) | Example torque at K = 0.20 (N·m) |
|---|---|---|---|---|
| M0.6 | 0.15 | 0.166 | 0.074 | 0.0089 |
| M0.8 | 0.20 | 0.295 | 0.132 | 0.0211 |
| M1.0 | 0.25 | 0.460 | 0.206 | 0.0412 |
| M1.2 | 0.25 | 0.732 | 0.328 | 0.0787 |
| M1.4 | 0.30 | 0.983 | 0.440 | 0.1233 |
| M1.6 | 0.35 | 1.270 | 0.569 | 0.1821 |
| M2.0 | 0.40 | 2.073 | 0.929 | 0.3715 |
| M2.5 | 0.45 | 3.391 | 1.519 | 0.7595 |
| M3.0 | 0.50 | 5.031 | 2.254 | 1.3523 |
| M4.0 | 0.70 | 8.779 | 3.933 | 3.1463 |
| M5.0 | 0.80 | 14.183 | 6.354 | 6.3538 |
| M6.0 | 1.00 | 20.123 | 9.015 | 10.8183 |
Computed from As = π/4 × (d − 0.9382P)² with ISO 261 coarse pitches; proof stress 640 MPa for class 8.8 per ISO 898-1. Values are rounded for display. The interactive tool above reproduces every cell.
Reading the numbers
Why the small sizes behave differently
Forces are measured in single newtons
At M1.0 class 8.8 the full proof load is under 300 N — about the weight of a phone. A torque wrench is the wrong instrument at this scale; driver repeatability, not wrench accuracy, decides whether the joint is loaded or stripped.
K dominates everything
Moving K from 0.15 to 0.25 moves preload by two thirds at constant torque. That is why the finish is specified with the joint: the coating is the friction, and the friction is the preload.
The mating thread is the real limit
In an aluminium wall or a plastic boss, the casting or the boss strips long before the screw does. The calculator sizes the screw; the joint decides the torque. Test on the real joint before anything is frozen.
A calculator sizes the screw — the joint sets the number
Send the drawing with the mating material and finish, and the friction coefficient can be measured on the actual finish instead of assumed.