There is a difference between gripping strength and pinching strength. Bathroom scales allow for pinch strength tests but not gripping strength. They are however both important as is the extension strength of your fingers and thumb.
Examples of each:
Grip strength - squeezing a tennis ball or someones hand.
Pinch strength - carrying a brick or free weights by pinching it between your fingers and thumb.
Extension strength (flexion exercises) - placing a rubber band around your fingers and thumb, then spreading them apart.
Mike