It is recommended that you replace the O-Ring for the Quartz Sleeve each time you replace your lamp(s). Be sure you order enough for all of the Quartz Sleeves on your unit. If you have a 75-watt unit, you will want to order 1. If you have a 150-watt unit, you will want to order 2. If you have a 300-watt unit, you will want to order 4. It’s always recommended to have extras on hand just in case.