Everything I have read as well as all of the factory threaded model 10s I have are indeed 5/8x24
I know a local silencer shop threads barrels to several "5/8x24" dimensions offering 5/8x24x.400 or 5/8x24x.500
Which one is the standard used in most US firearms applications I couldn't tell you right off the bat.
If I had to guess though I would think they shipped the wrong brake.
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