This summer I've tried helmet diving and it impressed me so much. Helmet diving is like a time traveling and spacewalking at the same time. There are not many technologies or equipment left without any modern changes throughout 100 years. 

Three bolt equipment is the one. Exactly the same suits were used 100 years ago.

Three bolt equipment, (Tryokhboltovka) consists of an air-hose supplied copper helmet that is fastened to a corselet and waterproof suit by three bolts which clamp the rubber neck flange of the suit between the metal flanges of the bonnet and the corselet, making a watertight seal between the helmet and suit.