It’s a bump stop for the rearend. Placed right above the pinion on the rearend.
When you tromp down the loud pedal the pinion wants to rise. When it does it bends the springs upward. The springs being springs want to stay straight and push the pinion back down. The pinion continues with this up down movement until you take away the power. The up down is your wheel hop.
A pinion snubber stops that first pinion rise and doesn’t allow that continuos motion of the pinion. Your tires stay planted and no wheel hop.
Some vehicles have bolt on snubbers that attach to the rearend. Mopar are like that.
You can easily build a bracket that hangs down to the top of the pinion that has a bump stop on it.
I’ve actually used a soft hockey puck as a bump stop.
Here’s a quick video to show the flex and pinion action.
https://m.youtube.com/watch?v=93v608LvmIY