The belt would have been marked on the outside if that is no longer visible it is probably easier to take the belt off and take it along to a local belt supplier who should be able to sort out a replacement.
Or give Boxford a ring on 01422 324810 see http://www.boxford-software.com/spares/X10Guard.html and if I'm correct the belt is a SPZ-737, "Z" section
If I had the option which I don't I would replace the linked belt on my Boxford AUD with a "normal" one but it has to be split to fit.
Edited By Bob Brown 1 on 21/07/2014 18:28:36
Edited By Bob Brown 1 on 21/07/2014 18:42:33
Edited By Bob Brown 1 on 21/07/2014 18:48:58