This 250g reel of bare copper wire is 26 SWG (24/25 AWG) gauge, measuring 0.018" (0.46mm) in diameter with an approximate length of 550 feet. The wire is sold by mass, so actual length is approximate. Bare copper wire is used in physics and electronics experiments including electromagnetic coil winding, circuit construction, resistance measurements, and demonstrations of electrical conductivity. The fine 26 SWG gauge is well suited for winding solenoids, transformers, and electromagnets where a high number of turns is needed in a compact space. Copper provides excellent electrical conductivity and is easy to work with — it bends and wraps cleanly around cores and forms without spring-back. The 550-foot reel provides enough material for multiple classroom experiments or extended project work.