When used near magnetic compasses, cotter pins must be made from which material?

Cotter pins used near magnetic compasses must be made from corrosion resisting steel due to their properties that minimize magnetic interference. Corrosion resisting steel is formulated in such a way that it does not significantly affect or distort the magnetic field that compasses rely on for accurate navigation.

This is crucial in any application involving magnetic compasses, as materials that are ferromagnetic or highly conductive can cause deviations in readings, leading to navigational errors. The use of this specific steel helps ensure that there are no disruptions in the compass's performance, providing more reliable and accurate directional information.

Other materials, while they may be suitable for general uses or non-magnetic applications, just do not meet the necessary standard for proximity to magnetic compasses. For example, aluminum alloy could still react in the magnetic field, leading to potential inaccuracies, and plastics, while non-magnetic, may not provide sufficient strength or durability needed for a cotter pin's functional requirements.