The best pack belt for the Nimbus Ozone belongs to the belts that go with their sturdier line of packs. The Nimbus Ozone is in their "Ultralight" packs. the next line is the "Light" packs. They have two styles of belts in that line -- one that is dimension wise the same height, and depth of the "Ultralight" belts but with the difference that a stiff spine buffets the back of the belt. These belts (both Ultralight and light) have a axle "hole" in the center back of the belt that a phillips screw goes through the belt to attach to the frame. With the "Light" belt, the frame connects to the belt via this spine, and the belt spine disperses the weight of the pack to nearly 300 degrees around the waist, so that you don't feel the weight of the pack only at the back, but around you. It's a significant dispersion of weight of the pack for almost no cost in weight.
I am a little overweight and needed to swap out my belt anyway, I opted for this "light" belt instead and got the Large size belt, but dimensioned the same as the Ultralight default belt but it has the stiff spine. Here is from the Granite Gear catalog that you can download:
"Light Pack Belt
All the features of the Ultralight Belt plus a high-density
plastic exoskeleton that forms a wishbone shape to cup
around your hip crest and add load-bearing support.
When fit properly, this exoskeleton forms an effective
“wrap” around your hips which helps to keep the belt
positioned right where it needs to be to effectively transfer weight. This belt is standard equipment on all the
Download this document to see what I'm talking about:
Be sure the new belt you get is the newer style where to tighten the belt, you pull the straps towards the belly button (the older belts, you pulled the straps AWAY from the belly button).
I looked at the manual, and could not find the difference in the belt dimensions other than "ultralight" and "light" and between them "men's" and "women's" and between them, "s","m","l". I wonder if the difference is that maybe a woman's belt is higher (up/down height) than a man's belt. I think I have the man's belt, light pack line style, size large (new style, where tightening means you pull the straps towards the belly button).
I just love the pack. Fantastic. One word of advice, go to a hardware store and get spare stainless steel screws for the pack and bring along a philips screwdriver (either in a knife or keychain setup), I did one time have a screw come loose -- I had the pack repaired and I think the tailor (at a local store) did not tighten the screw tight enough and the belt where it met the frame, the screw came loose and due to having a spare on hand with a screw driver, I was able to fix myself in the field (on the trail). Thank goodness. My spare screws were stainless steel so they would not rust. The pack has a spare parts pouch that is clipped underneath the hydration pouch, look for it -- I put the spare items in that pouch.
You might be able to get the spare screws from GG when you call them -- ask. Let me know what you find out.