If I understand the locking mechanism correctly, you screw the tank in tight and then turn it some more to move the tank around the carto which is held still by the mod. To me, this is a horrible idea. It pretty much requires overtightening and makes messing up your center pin a huge risk. I just don't bother with it and only screw it in until I get a firm connection. It doesn't affect the performance on the tank any and despite my gripes about the design, I have no issues at all with the performance of the tank. I actually like the performance better than the UDCT. Just wish they didn't put in that gimmicky locking thing.