This electromagnet is great for simulating assembly lines or adding to a robot!

Power: 12VDC@330mA
Model: ZYE1-P25/ 20 
Thread Size: M4
Holding force: 11 lbs/ 5kg (perhaps with a perfectly flat highly ferrous material)
Diameter: approx. 25 mm 
Height: 20 mm 
Cable length: approx. 20 cm 

Included: 1 x Electromagnet