I was lucky enough to pick this tool up from Phil at the IPMS National Convention in Omaha during the Reviewer Corp get together.
The text below was taken directly from the UMM web page and explains the Micro Mitre Box details better than I could:
MICRO MITRE BOX - MN048 XL (45° 90° 60°) cutting slots.
High Quality - MMB box with adjustable stop 110MM x 20MM x 14MM
- This aluminum micro mitre box is just 110mm long making it ideal for miniature work.
- Each unit has one 45 ° degree, one 90 °degree and 60 °degree angle cutting slots.
- For use with original JLC/CMK/HAULER razor saws (JLC001, JLC002 and JLC004 - thickness saw 0.12mm).
- It is used to cut square ends, perfect splices and mitered corners.
- The miter box has an adjustable stop.
We highly recommend this tool to all modelers who owns mini saw blades.