Our bubble plate assembly 4 inch comes with a sight glass, bubble plate, clamp and bubble plate gasket. The units are modular and can be stacked on top of one another. The more plates you have, the higher the proof output. Four plates will get the proof up to around 170. Six plates will get it up to about 185 proof. Made from durable 304 stainless steel, tempered borosilicate glass, 100% red copper and 100% silicone for the gasket.