Paul,you can get some more info from Theoben USA,if you do a search you will be able to find the full history of the Theoben Gas-Ram! Theoben wasn't the original founder of the gas-ram,in 1975 Shark Manufactoring started the gas-spring for underwater spear guns,I believe it was 1979 when they actually patented the gas-ram in Argentina,in 1981 patent was granted in the U.S. It was after that when Theoben designed their own gas ram & mastered it,the gas ram process became to expensive in Argentina & they discontinued the gas-ram.