These are typically included within the 2% parts sundries allowance. This is currently set at a default of 2% but this figure can be adjusted, or indeed a fixed sundries cost can be entered in the rates screen. This is to cover the cost of workshop consumables that are used in non merchantable quantities. These items may include low cost nuts, bolts, washers, fixings etc., that might be required for the completion of the repair.
The definition of low cost may be determined by your work provider within their menu pricing structure.