Viscous Fan Coupling Tool (1pc) for Land Rover Discovery 3 & 4 pair In theory you need an In theory you need an M8 rivnut fitting tool to fit these captive nuts but if you drill a hole and ensure the rivnuts are a tight fit and can't spin then in practice we find we can hammer the rivuts into the hole and then fit the step and the rivnut will tighten inside the chassis as you tighten the bolts These looms will allow you to install the later type (2012 14) headlights to the earlier vehicles (2007 2011) This item WILL fit the viscous coupling on all Land Rover Discovery 3 TDV6 Diesel Models This tool also fits the fans on many other Land Rover vehicles and is essential for any workshop working on Land Rovers