Wanhao Branded Magnetic upper Mat 420mm x 420mm size. These stick on the metal sheets on the 3d printer bed.
These mats are for use on Wanhao D9 400 mk1 3d printer which has a 400x400mm build area, or on i3 plus mk2 3D Printers which have 180x180mm area.
For the i3 plus mk2 which uses a 200x200mm mat, you can buy this large mat & easily cut it into 4 equal parts.

For older version which doesnt use the magnetic sensor, please buy the other BuildTak style bed mat.

Works extremely well for most materials like PLA, ABS, PETG, TPU etc.