Mikey.. Sorry to say it but you are wrong on this one.. (unless Slingerland were purchasing hardware from Pearl). and I'm not aware of that.

I bought mine mid 70's from the Aussie Pearl distributor and at the time I was working for them as their Stock Controller and doing their purchasing. I just pulled one of mine apart (as a point of interest) and it looks like it came from the same die as yours from your pics..

Cheers

John