The GMC CCKW

Remember, the original WWII Issue Radiator Cap your truck left the factory with had no rubber seal on the bottom of the pressure valve, the portion that contacts the ledge that is at the inside of the filler neck. Instead there was a fibre gasket that was placed inside the neck for the pressure valve to seal against. If you are using a replacement cap with the rubber seal on the bottom of the pressure valve, the fibre gasket should be removed. The original WWII type gaps will not function if the gasket is not in place.
Joel

The CCKW Cap that GMC installed was rated 4# and had a handle on it. Other than that, it is the same as MB/GPW and 4 Ton Diamond T. NOS CCKW Caps still show up here and there, I may have one or two. They are easier to remove and Install because of the handle. Without the handle it is tough to get a good grip because of the Radiator Tie Rod.