Wera Imperial & Metric 9-Piece Allen Key Skadis Holsters

Designed for use with 3x3 magnets, though you can size them up in the f3d file if your magnets are weaker or a different size. 

If you're seeing the other Skadis holders in this image and want those instead, check my profile. 

Designed for use with T-slot nuts. I personally like these, but in theory you can use whatever