4" Clear TC CapProbably the coolest add on for your new FLEX! We've heard many brewers who have switched from clear carboys to stainless and they only have one complaint; I can't see my beer fermenting any more! Brewers are curious by nature and we're not ones to stop that curiosity so here is our solution to that problem. Our engineers designed a clear polycarbonate (same material as bullet proof glass) cap which allows you to see inside the top of the FLEX when