Here are some measurements of a ZipZap motor vs. a Sen Fa Char-G clone motor...

ZipZap motor is:
6.04mm diameter
12.21mm length (total can length, not including shaft or contact)

Char-G clone motor:
6.04mm diameter
12.14mm length

I have had no problems using ZipZap motors in my Char-G clone.
This may not be true with a "real" Char-G or MicroSizer.