A stainless steel Tri-Clamp Cap with 3/8" Barb fitting.

Tri-Clamp Size: 1.5" (3.81cm)
Made from: 304 Stainless Steel
From: Ss Brewtech

Tri-Clamp (also called Tri Clover) fittings consist of 3 parts: the clamp, the end piece and a silicone gasket. Used in most commercial breweries they are very sturdy. With no nooks or crannies for bacteria/yeast to hide, they clean like a breeze.You can see every surface that meets your precious wort. If that weren't reason enough: they don't leak.