67 soft top mounting bolt finish

[Randy R.]

Re: 67 soft top mounting bolt finish

Mine have the same head marking.

[Chuck S.]

Re: Black Phos, Bolt and Captive Washer

Mike, in my experience, phosphate (on Corvettes) varies from black to dark gray to medium gray. My understanding is that the color is determined by the type solution used and the time of immersion. Color may also be inflenced by the strength of the solution; i.e. as the solution is "used up", it must be replenished or the color begins to "fade".

Black phosphate, however, is typically done with manganese phosphate solution, and the gray phosphate results from zinc phosphate solution. If the specifications called for phosphate finish without specifing the solution type, it is possible that the color varied from the same supplier depending on whichever chemical was cheapest or more available at the time. If the subject bolts have different head stamps (from different suppliers), then it is likely the suppliers used different solutions to provide the phosphate finish.

All of the above is speculation, but it's offered as a plausible explanation for observed differences in phosphate part color.

[Michael H.]

Re: Black Phos, Bolt and Captive Washer

Ok, that would explain the different colors. I see a lot of parts in these cars that are grey instead of black but never knew what the actual difference was in the plating process. Thanks Chuck,

Michael

[Mike M.]

Black Phos looks more like dark grey primer.....

same finish as the top and bottom window channel cross recess bolts in the rear door latch area, the retaining screws in the cowl vents and tire tub bolts to name a few areas, there are others.