Features:
Works well with Anet A8 Prusa i3.
Pretty solution for auto-adjusting heatbed level. 
10-30V DC working voltage, output NPN.NO.
Comes with mounting plate & screws, pre-soldered connector, so no wiring is needed.
Just unplug the original z stop and plug in sensor and screw into the back of printer.

Specification:
Shape: 18 * 18 * 36mm
Detection Distance: 5 mm
Operating Voltage: Within DC 10-30VDC
Output Mode: NPN three-wire normally open
Output Current: 300 mA
Package Weight: 76g
Quantity: 1pc

Package included:
1 x Auto Leveling Position Sensor
1 x Plate
2 x Screws