Do you need new castors for your AC 5 Work Lowback? The braked castors are part of the original construction of AC 5 Work Lowback. They meet the highest quality standards and are characterised by accuracy of fit. Castors are available for different floor types – hard floors (e.g. wooden floors) and carpets – and are sold individually. In most cases, Vitra recommends replacing all the castors on your product at once to ensure a smooth and consistent rolling movement.