Genuine Wanhao Branded lower metal sheet to be stuck on the printer platform, on which you can then use magnetic mats & magnetic sensors. This is used on Wanhao i3 Mk2 (also called i3 v2) 3d printers, the new version of D5s, & other such machines.
This is not the actual print surface, its the metal sheet on which the build surface sticks magnetically.
For older version of the i3 please buy the other BuildTak style bed mat which has glue on one side.
Works extremely well for most materials like PLA, ABS & PETG.