A superconductor magnet held by Wesley Crusher
A superconductor magnet was an extremely powerful magnet.
In 2365, the allasomorph Salia correctly identified a superconductor magnet that Wesley Crusher was carrying as he walked past her on the USS Enterprise-D. She warned Crusher to be careful with the device as it could, "rip the iron right out of your blood cells." (TNG: "The Dauphin")
The superconductor prop was later reused as the spatial trajector matrix in VOY: "Prime Factors".