I do not know what the material is but are we talking Magnetic level indicators as used in the likes of the vc10?
That was a rod in the wing tanks that was on like a half turn to unlock, it dropped out of the bottom of the wing until a metal tip reached a circular donut shaped float with a magnet incorporated in it floathing on the fuel, this was then read off the stick as inches of fuel, you then calculated the nose down angle and wing high / low angles using a couple of scaled spirit levels built into the fuel panel compartment and a chart on the VC10 was used to correct the inch figures to allow you work out an accurate quantity. Each tank could have several sticks and depending on how it sat determine the ones you used.
similar was a drip stick, this was hollow and you lowered it until fuel dripped out thus indicating the level, you then took readings as per above.