The Bigbox heated bed is a 300x200 bed backed with cork and is supported at each corner. Alas, it sags a small amount toward the center. These are designed to provide a little support at three positions underneath the center of the bed.
Fully closed, the bolt will be 22mm. The bed itself is around 25mm distant from the platform below, but could be slightly lower or higher as a result of levelling using the corner spacers. Unscrew this slightly to fit your needs; it should happily support as low as 22mm or as high as 28mm.
HeatedBedSupport-Bolt.stl | 847.7KB | |
HeatedBedSupport-Nut.stl | 885.4KB |