Here are a range of fitting suitable for IBC storage containers. We sell fittings for two IBC outlet sizes: 2 inch (60mm) and 4 inch (100mm) IBC Buttress threads. Respectively, these are also called S60 by 6mm and S100 by 8mm buttress threads. The 6mm and 8mm sizes denote the thread coarseness, measuring the thread from peak to peak.
Carefully look at sizes and specifications before ordering. This youtube video will advise you on how best to measure the size of your IBC outlet to make sure you have the correctly sized fitting: http://www.youtube.com/user/SmithsDeanDrums