The Science Source 14824 air core solenoid. The solenoid is wound on an air core in 5 layers with approximately 560 turns of #16 Cycled solid copper wire. The number of turns per unit length for each coil is 3720 turns/meter and results in a calculated field to current ration of .00486 Tesla/amp. The inside diameter of the coil is 3.2 cm. Each coil is designed to carry 5 amps continuously, and up to 10 amps for short durations. Comes with instructions new in box.