I have tossed the stock belts on all my lathes, the one on my PM-1340GT quickly through black chunks everywhere. I have been using the Gates Tri-Power notched belts on several machines and they have lasted years and still look new with almost no debris. I am sure there are other belts that will do just as well. Measure up the current belt and compare the specs as to OD and ID of the belts, they are not necessarily interchangeable based on the belt designation length. As to D1-4, the most common range of lathes that come with this size are 1236-1440, and 2-5 Hp. Almost all larger lathes would have a larger spindle bore requiring a larger mount then D1-4. The Monarch 10EE came with a D1-3 and used a 5 Hp spindle motor. The PM1228 D1-4 is a retrofit to the original design that if I recall was a bolt on mount.