RUBBER WELL NUTS ( 0 Reviews ) Review this item Rubber well nuts with threaded brass insert.Comprise of a flanged rubber sleeve with captive brass nut.Offer excellent electrical isolation & vibration resistance.No special tools required. Simply place the fixing in the hole, insert a bolt and tighten to expand the sleeve.Ideal for fixing to cavity walls & hollow blocks.The grip range is the thickness of material the nuts will tighten into, thinnest to thickest.Can be used with most types of bolt. Sizes given are thread diameter x fixing length.