Hello

I have a question for those who own a Mamiya 645 system:
Could you please tell me the dimensions of the film insert, just the insert.
I'm looking at using the insert as part of a custom pinhole camera I'm building.
Also: Do the film rolls 'lock' once the film has been wound into place or do they remain 'loose'. So the insert could be used on it's own and film drawn from the roll to the take-up roll?
The insert would be used just as a 'film holder' and not a 'winder'.
Thanks for your help.

David