The two types I have came across in 4x4 GS, RFVS and 6x6 are the 1/4 turn similar to a bayonet fit and normal VDO screw mount, the later I much prefer because it is much easier to make a seal, also there are some VDO screw mounts that have a sandwich plate, where you don't remove the screws just loosen them, the internal sandwich plate has indents so you can then maneuver the sender to remove it from the tank.