Apparently I can hold on to heavier dumbbells than others, but they can crush my hand much harder in a handshake. This tells me that support grip and crush grip can be very much apart. I believe there's not really a carryover from gripping strength to bar holding strength. I can only close the Trainer gripper, about 100 lbs. for a few reps, and my hands and forearms are dead. 

I can, however, hold on to a 200 lb. dumbbell for a few seconds (one-handed). 

I can also hang from a bar with almost my bodyweight added (200 lbs. + 200 lbs. = 400 lbs. of hanging support).

However, I know a guy who can't do either of the prior feats, but his grip in a handshake is quite impressive (overpowers mine). He also can't close much more than me in a gripper, but has a strong crushing grip.

My main question is, how does crushing grip differ from support in a muscular sense? Aren't they both the same recruitment of muscles used to close the hand?

How is it supposed to make sense that I can barely squeeze together a 100 lb. gripper spring, but can hold on to a 200 lb. dumbbell handle? Or support 200% of my weight hanging freely from a bar, but fail to crush an apple with my dominant hand?

I always hear people telling me I'm not too strong with my hands in handshakes for some reason (my grip strength is about average for an adult male in crush PSI), but average men can't hold a 200 lb. dumbbell in one hand. Anyone here could explain how the hand strength varies so much in different lifts (e.g. crush 200 lb. gripper, can't hold on to a 200 lb. bar, or hang with 200 lbs. added to bodyweight, but can't open a jar of pickles)?