A pair of precision coils with 4mm terminals. 400 turns of copper wire are wound on a former of about 150mm diameter. The coil is comprised of a support rod which fits on the holders of the track system supplied enabling them to be aligned on a common axis for measurements and the study of the magnetic fields. Normally used in pairs each coil has 4 mm terminals and their distance apart is adjusted over the track supplied. The maximum current in the coil is 1A to avoid overheating. Direction of current is marked on each coil. The minimum & maximum distance the coils can be apart is 44.5mm to 305mm (1.75"" to 12""). The overall dimensions are (H)165mm x (L)280mm x (W)165mm (6.5"" height 11"" length 6.5"" width).