A method of manufacturing cracker roller discs comprises forming a disc blanks and machining to produce the final form. The disc blank has an axial bore through the centre, a first portion radially outward of the centre of substantially constant thickness, a second portion radially outward of the first portion which second portion tapers towards the periphery of the disc blank, and a plurality of upstanding ridges extending radially outward across the second portion on opposed faces of the disc. Machining, suitably by turning on a lathe, removes the top part of each ridge and leaves at least one sharp edge extending along it, with all ridges on a face being machined in a single operation.
