Graphite

Graphite is the best material to work at high temperature and at the same time is the softest ferrule. Therefore it fits the capillary column and seals effectively at only ¼ turn past fingertight. As this is a very soft material, thery are easily destroyed or deformed. Ideal for FID and NPD detectors. 
Do not use with MS or other oxygen sensitive detectors. 
Upper temperature limit 450ºC.