Magnetizing and demagnetizing screwdrivers and screws

Small screws that you can drive directly into hard-to-reach places with a screwdriver.

An indispensable work aid.



And a screwdriver can be magnetized quickly, for example, with a tool like the one in the picture on the left, which can also demagnetize screwdrivers. However, if the screw itself is already magnetized, this cancels out the effect.

On the right, you can see a choke for demagnetizing tape heads in magnetic tape recorders. However, its magnetic field is too weak for metal parts, at least that's what my tests have shown.

What are your recommendations for demagnetizing screws and screwdrivers?

I use exactly the same tool (the red one on the left).

I use a magnetized screwdriver to position very small screws that I can no longer position with my finger when screwing them in. A very useful tool.

There are demagnetizers that run on mains power. Does anyone use them, and what are their experiences with them?

And how can I demagnetize screws?

De-magnetizing works by going around the hysteresis loop while progressively decreasing the excursion. In other words, submit the magnetic material to an alternating magnetic field, while decreasing the amplitude to zero. This could be done with a solenoid powered by 50Hz AC, and either decreasing gradually the excitation to zero, or withdrawing the screwdriver from the solenoid.
Disclaimer: that is from university physics; a working device would require some experimenting and optimization.

Also: do not let a magnetized screwdriver come close to shutter (or aperture) blades