Glass Tube covers are used on all small "pencil" style halogen lights. These tubes will older Rena Mini-Lights and newer 10 watt lights as well. Replace when broken or if they become too cloudy from mineral deposits and algae. Model GT-9V fits older Rena Mini-Lights ML9V-RP and newer 10 watt Rena Lights. Approximately 9/16 outer diameter.