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by the way all the pictures are of the same rim
...I noticed that next to the valve stem was stamped m48 but the inside had m18? kind of thought that unusual for code stamping, as I would assume that stampings would be the same number if referencing a date or application?
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Makes perfect sense- Wheels were made in 2 pieces. The outer rim and the inner part. Those dates are for when each part of the wheel was made, not when the wheel was assembled. The assembled date are the numbers on each side of the valve stem.