We recommend you use a toothed collar washer with the lowest possible collar height. When tightened, the nut or bolt ‘sinks’ into the Dubo toothed collar washer. Using the lowest possible washer will give the tool used to tighten the nut or bolt more area to grip the nut or bolt. The height of the washer has no effect on the functionality of the structure. See this drawing for a visual explanation.