Holder for a hole saw with switchable blades. Base is a 2x4 gridfinity grid. Fits:

The adapter (70mm)

The drill bit (8mm x 100mm)

6 Blades sizes: 25/26 - 32 - 40 - 45 - 54 - 65/66 (size different per manufacturer but both fit). 

For bigger saws see:

https://www.printables.com/model/1089451-gridfinity-big-hole-saw-holder