It's about 1/4 ". I've seen narrow ribs and standard wider ribs on gauges 12 through 20. I don't have a 28 or a 410, so I wouldn't know. I have 16's with and without. I don't think it makes any difference in target alignment but the narrow rib looks nice .
By the way, as an upland game bird hunter, the 32" barrels are too unwieldy for me and swing too slow. I've shot Kansas pheasant with it, once, then back to the 28" 16. It's nice for trap though.
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