I'm just about to rebuild my adapter from scratch. I've bought a quite heavy Canon F1.4 and one thing that worries me is how it should be attached to the adapter. I won't be using any other SLR-lenses. The adapter will be a NIVEA-spinner built into a plastic box.

The solutions I've read about here are the following;
* using a rear lenscap
* using the mount from an extension tube
* manufacture a custom mount in metal (not an option for me)

Are there any other ways? I've had some thoughts about using some kind of hose clamp. Does this sound like a stupid idea or has anyone tested?

A lens cap is flimsy and won't be accurate in terms of distance to film plane.

An extension tube mount is perfect, and you can get them in short lengths so as not to require hacking it up to shorten it. The price and/or amount of work to manufacture a mount out of metal (especially one with a locking ring) is ridiculous compared to a $10-15 extension tube.

Even if your box is made in such a way that you need an extremely short extension tube, it will be much easier to sink the tube into the box (or remake the box) than to make a custom mount.

Nikon BR-3 for $35, and if you need an extension tube, ThorLabs SM2 2" round tubing ($35), with a male/male 52mm-58mm macro coupler ($10) to join them together.

Wayne Kinney just gave good idea about it: http://www.dvinfo.net/conf/showpost.php?p=467590&postcount=4

But if it has to be designed that You change lens with different mounts frequently, then my advise is: lathe to Your adapter C-mount and use adapters to different bayonets. John Wyatt started and fullfilled very useful C-mount thread:
http://www.dvinfo.net/conf/showthread.php?t=62138&highlight=c-mount

related products:
http://www.edmundoptics.com/onlinecatalog/DisplayProduct.cfm?productid=1459
http://www.srbfilm.co.uk/pdffulllist.pdf

Jim, the Nikon mount won't work with his Canon F1.4. There are, however, Canon reversing rings too, such as this one:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7609417045&category=30059

Sorry I missed the Canon part, just read the topic and posted.