Max thickness for a waterjet depends on the pump horsepower and what orifice/mixtube the machine has on it. I know I can comfortably cut 4" and less on a 30HP machine with an 0.011" orifice and 0.030" mix tube. That same machine did successfully cut through 6" thick, but the cut started to wander and lose its edge quality after 4".That's super work! I knew it couldn't be waterjet as about 3 inches is the max. I thought possibly EDM as I blew the photo up and didn't see any signs of flame work. All I can say is you have some fantastic equipment and some fantastic operators.