Rounding error. 28.575mm is within .025mm of what you want or about .001". I doubt that the tubing itself, or the derailleur clamp inside diameter, is held to that accuracy and a coat of paint on the frame tube could be thicker than that.
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Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
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