Magnetic Needles, 100 mm-EIS-PH0816C offers a thoughtfully designed, durable resource for hands-on learning. Single, magnetic needle Needle measures 4" (100mm) long Made of carbon steel Features brass cup bearing for pivoting Great tool for physics classrooms Excellent for magnetism experiments in physics classrooms. Single, magnetic needle. Made of carbon steel. Features brass cup bearing for pivoting. Needle measures 4" long (100mm).