This is a 12V DC electromagnet with a 30kg lifting force.  A lifting solenoid electromagnet consists of an iron core and a coil to attract magnetic substances, using the magnetic action induced by electric current, only while the current is applied. 

Note: Images seen may be different from actual product in terms of dimensions

Precaution

• Electromagnets are specified with a "holding force" of say 30kg.
• This is not how much weight they can pick up!
• Divide the holding force by about 5 to get a rough estimate of how heavy a thing it can pick up.
• So in this case, about 6kg max.
• Note that pick-up weight also depends on a flat surface, maximum surface contact and the ferromagnetic metal content of the object to be picked up.
• A perfectly flat steel cube will work great, something oddly shaped or covered in rubber or plastic will not!

• Model : KK-P40/20
• Thread Size : M5
• Operating Voltage : 12V DC
• Power Consumption : 3.5W
• Holding Force : 30kg 
• Total Diameter : ±40mm
• Centre Diameter : ±18mm
• Cable Length : ±250mm
• Height : ±20mm