Equinox 800, Garrett AT Max, Garrett AT Pro, with stock coil
AT PRO Pointer, NEL Storm coil, Garrett 5 X 8 coil, 9 X 12 Garrett concentric coil, Nel 6.5 x 9 coil for the Max
Clip from bib overall I would say early 1920's or so. Pioneer made a lot of work clothes, and if not mistaken they are still in business making safety work gear.
I think it is a suspender related piece from a set of "pioneer" suspenders, I wouldn't call it a buckle
but more of a supporting clip to the set, much like these