Sonny,?
There is nothing authentically American about using imperial fasteners.?
As to why Losmandy uses imperial fasteners I think they were more widely in use by American machinists at the time the mounts were designed and machinists like everyone else tend to use what they know.
Why Losmandy continues to use imperial fasteners I am fairly sure has to do with economics and ease of continued support.?
Neither of these has much to do with being authenticity American unless you are talking about being pragmatic.?
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Chip Louie - Chief Daydreamer Imagination Hardware
Chip Louie