Van Cor Threads can have different volumes of space from one end to the other

The differences in the volume of space at the two ends of the concave or convex thread used underwater has a hydraulic component. The initial contact end has the smaller volumn. The other larger volumn end engages at a quicker rate. All surfaces come together are at their terminal position. Assembling under water will create an acceleration of the fluid that will hydraulically pull water out of the threads as they close.