Hi Mick, flat belts for machine pulleys were usually joined with the wire type clips in the photo below and as peak4 has shown, were closed in a tool in his photos.
The tool in peak4's photos however, was probably a more expensive one. Mastabar also did a simple machine like the one below.
In this one you could do four different sizes. You simply cut off the required number of clips needed for the width of the belt, bearing in mind that each group of clips at each end had to be offset so that the ends of the belt would be in line with each other. You would then load up the clips for one end into the correct set of slots, first by removing the pin with the eye on the left hand side and then putting in the clips and replacing the pin back to retain the clips in the correct position. With a bit of experience and if the width of the belt would allow, you could do both ends at the same time.
Once you had all your clips retained, you would rip all the paper out that holds the clips together for loading into the tool. You would then push the belt end into the open clips as far as it would go and then close the hinged part of the tool whilst keeping the end of the belt in place.
Then when you were ready, you would clout the hinged part with a big hammer and one end would be done, you just repeat the process for the other end, remembering to offset it in the correct direction. The tool in peak4's photos would be the same procedure, but of course you don't need a big hammer.
Regards Nick.
P.S. instead of offsetting each end, you can also use one less clip in one end and the belt ends would be placed in the centre of each group of clips.
Edited By Nicholas Farr on 18/04/2016 00:26:30