Hi,
I have an Boxford AUD, and as the previous people have mentioned I use Brammer belt. How ever fitting can be a little diffucult, removing the top cover and the rear belt guard will ease the threading of the belt (three screws on the back guard, four on the top). If you haven’t taped the new belt to the old one to pull the new belt through.
Additionally if you fit the recommended 4.25ft of belt. You may find it easier to make the joint with the belt off the lower pulley. Then to fit the belt with out damage, slacken the four grub screws (two each end), remove the three allen cap screws holding the end of the counter shaft to the cabinet (outer end) and remove then casting. The counter shaft will now lift just enough to pull the belt over. Simple no straining. Hope it helps and happy turning.