MDF Wheel, 6mm thick fibre board, 54mm and come with drilled centre holes for 4mm dowel, There are also available in 54mm and 74mm or you can order a mix bag
Magnet Probe, Consists of a small 19 mm length alnico bar magnet mounted in freely rotating gimbal, rotates in 3D so that all x, y and z co-ordinates, three-dimensional magnetic force fields, can be mapped, Strong plastic construction