Use with plastic breather valves only. Large hole. Note: Steel breathers require steel breather valve spacers. Plastic breathers require plastic spacers. Do not intermix steel and plastic parts. Note: The OEM plastic breather is low cost but an inferior, poor quality product that will cause damage to crankcases in the breather bore since it is prone to distorting. The sooner this stock type breather is removed, the better. We highly recommended to replace it with a steel breather valve, like was used in earlier engines.