Fixed centre wheels are lower maintenance with no rim bolts to check and generally offer a higher strength wheel than a wheel with adjustable centre discs. They are available in two designs: formed disc or flat plate. Formed disc wheels are the stronger of the two (size for size) and generally use a 12 – 15mm thick disc, fully machine welded into the rim. Discs with different offsets are used to achieve the required track setting. Flat plate wheels may be used in place of a formed disc to achieve a specific track setting or for ultra heavy applications up to 50mm thick. Depending on the application, most plate thickness will be 12, 15, 20, 25 mm, fully machine welded on both sides into the rim.