The torque capacity of a hex key is a function of hardness, tensile
strength, and stock size. Hardness determines tensile strength, and
the following formula can be used to determine torque:
Torque = (tensile strength) * .2 * (stock size across flats)3
|
|
|
Example:
A hex key has a hardness of 57 RC, a tensile
strength of 320000 psi, and a stock size of 0.25 inches. |
| Torque = (320000) * .2 * (0.25)3 |
| Torque = (320000) * .2 * (0.15625) |
| Torque = (320000) * 0.003125 |
| Torque = 1000 lb.in |
The chart below shows the relationship between hardness and tensile
strength. |
|
|
