Keep standard taper glass joints from seizing, leaking or galling. No lubricant is required to make a vacuum-tight joint. The top of each sleeve has a rigid, knurled grip ring 3mm thick for easy assembly or removal of the sleeve from a standard taper joint. In addition the sleeves have outer rings on the taper which prevent sticking together. The sleeves are made of virgin Teflon® TFE. 2mm (.008"); thickness at rings is .35mm (.14"). They can be subjected to temperatures from -200ºC to +260ºC (-328ºF to +500ºF). The sleeves are resistant to most chemicals and are reusable.