This is a used Rockshox Reverb stealth B1 dropper seatpost.

Stealth means the hose is under the seatpost and must be routed through the frame.
B1 is the second generation post and does not have an air bleed valve under the saddle clamp.

This post includes a right hand side plunger style lever and a 56 inch long hose.  This lever can be installed on the right above the handlebar, or on the left side under the handlebar.  

The lever is pre-bled and works out of the box, but you will need to disconnect the hose to install the seatpost on your bike.   You may need to bleed the lever after installation.

Dropper post diameter:  31.6mm

Travel:  125mm

Hose length:  56 inches  (that's pretty long, should fit most large and XL bikes)