This adapter is designed to connect my SIEMENS vacuum cleaner to my Makita Router. I'm sure the vacuum cleaner connection is standardized.
The diameter from the two sides are:
Vacuum side:
Outer-Ø 30,8mm
Inner-Ø 24,8mm
Makita Router:
Outer-Ø 37,2mm
Inner-Ø 43,2mm