Here we have 3-D printed magnet rings that will clamp onto the differential input flange to provide the pulsed input signal to allow variable speed control of electric power steering. Photos left and center are from Dominic Clancy . This ring has nests for four square magnets. Magnets are available on eBay and cost peanuts for ten. Search for "Block 5x5x5mm Cube Strong Neodymium Rare Earth Magnets".
 
Photo on right is from Colyn Firth in Doncaster, South Yorkshire, UK. He had them made to the same basic design, but to accept 5 or 6 magnets.

Dominic has provided this drawing for a bracket to attach the hall effect sensor to the top front rib on the differential.