Only came up with examples that were clear for Dearborn examples. Given how close and because they often shared the same suppliers for other parts I think they would be the same
On used or aged originals it appears that they were likely zinc but we know that dichromate doesn't hold up well over time and I think they were zinc dichromate. Sure if that statement is incorrect someone will offer that opinion.
Examples from two different cars.
Three examples from another car
And finally examples from a very low mileage (just over a thousand miles reported) example
Hope these help