Is it the Tenax I, like this?
You might at least estimate the dimensions from that photo at Flickr.
Or, it looks like you could wind the film into a take-up cassette instead, if you can't make a spool fit well (of course, there's still a spool, in the cassette, but I suppose the cassette will steady the spool somewhat). I have a Voigtländer Vito that came without a spool, which works fine with two cassettes. You have still somehow to attach the film to the spool of the 'uptake cassette'; I use an old Ilford one which has ends that pop off easily, and use a scrap of tape to attach the film.