MK2B LED Kit - LEDs and Resistor
This kit contains two 0805 SMD Red LEDs, and one 560Ω 0805 SMD resistor.
The 560Ω resistor was chosen to run the LEDs at 12V power at approximately 3/4 their rated current, both to keep them from being too bright and to extend their lifespan under hot conditions.
These components are suitable for most heated beds with SMD pads - including MK1, MK2A, MK2B, and MK3.
You'll need a fairly fine soldering iron tip to solder these, as they are SMD.