I think it was their first deep rim, or maybe it was their first clincher. t's just like the old 440 was replaced by the 400. Their old nomenclature had to do with the rim weight, on rims, anyway.

bump for a few more ideas?

The 500 was the original 650c size clincher rim at 58mm deep. These rims were produced between 1997 and ~2000 and are of a post-bonded construction with an aluminum hoop bonded to a structural carbon rim. They were replaced in 2000 with co-molded rims utilizing welded hoops bonded to a structural carbon rim during the initial molding process. The newer rims are much stronger and have machined braking surfaces for better overall performance and durability, plus they are lighter.

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Did Zipp make some ~60mm deep carbon rims with aluminum clincher hoops, rebadged by American Classic as Deep V?

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Yes. Zipp also made rims and discs for Blackwell, Velomax, and Bontrager also.

Oh, I also forgot a couple years ago they made rims for Cane Creek also. It had sweet blue graphics and titanium spokes.