This Comfort Center fits over our 683 Series ventilators (now obsolete). If you have a Freightliner truck built between 2002 and 2005 and you have not replaced our ventilator this Comfort Center should fit. We only have 8 pcs., so we are offering this at the very low price of $50.00 each. This part will be discontinued after we have exausted the current inventory, so order today to avoid missing out on this exceptional value.