These a great quality heated bed with a few extra features that you don't find on the more standard beds out there.
The first is that these are dual power and can be used with either 12v or 24v supplies, just choose the appropriate connection pads on the board.
These beds have the LED/Resistors pads pre-soldered to the side without the heating traces, which means you can have the heating traces facing upwards so they can most effectively transmit heat to your print surface.
A small hole in the very centre allows a thermistor to come through and be in direct thermal contact with the print surface so you can get the most accurate readings possible.
Finally there are 5 mounting holes, 1 at each corner, and another in the middle of one edge - this allows you to have either the more normal 4 point mounting, or alternatively a more easily levelled 3 point levelling system.
MAKE SURE YOUR Power Supply HAS 10 MORE AMPS SPARE!!!
- 200 mm x 200 mm active heated area.
- 209 mm center-to-center mounting holes (outside the active area).
- 214 mm x 214 mm total PCB size.
More information at http://reprap.org/wiki/PCB_Heatbed