it refers to the output of the tanks regulator.
high pressure = 850psi output.
low pressure = 450psi output.
the 68 is the size of the tank in cubic inches, and the 4500 is the pressure it holds air. theres lots of different sizes/pressure combinations.
almost every gun out there will work with HP, so its fine unless yours specifically needs LP. also a lot of mechanical guns like tippmans and spyders wont work with LP, they need the higher pressures since they were designed to be used with co2, which also tends to output around 850 psi.
ninja tanks are great, i love mine. great regs. plus if you do ever need to change the output its just a matter of swapping a few shims.
Last edited by Rebel_816 : 06-01-2012 at 04:13 AM.