Generally, grip strength is broken into three categories including:
Pinching — The use of the hand and fingers to produce a force that’s held outside of heavy forearm use. This is typically trained with things like plate pinches, which only include the thumb and fingers.
Gripping — The combination of our hand’s grip and forearm to produce force. This is often trained with pulling movements.
Crushing — The use of the hand and forearm to squeeze or crush something. This would resemble most grip training devices or grip specific machines.