This is the Bilstein 2.0" diameter Air Bump (aka: hydraulic bump stop).
It has a 4" stroke and is tunable & rebuildable.
Used by most of the competition vehicles for it's performance characteristics, it is perfect for additional suspension dampening control on a Jeep.
This type of bump stop is perfect for rock crawling and is recommended for high speed blasting.
Two bolt "pinch" style can "mounts" sold as a pair, but separately.
Click on the picture to see larger more detailed images!