? what headmark and bolt style is everyone finding on the lower plastic airdam on the frontend lower valance . This is the 2" plastic piece running the width of the car.
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Re: 69 airdam fastening bolts
Kelly------
The bolts were 1/4-20 X 9/16" and originally of GM #3856691. They were idented hex head, phosphate plated, and had a captive flat washer. Interestingly, they were of GM-275 material. This is indicated by a 3 line headmarking, but with the lines 90 degrees apart, instead of the radial 3 lines of 120 degrees apart used for GM-280 (SAE Grade 5) material. GM-275 fastners are rather unusual on Corvettes of the period. A common headmarking was "RBW" (Russell, Birdsall, and Ward).
These bolts were used in conjunction with a flanged nut of GM #3866846.
Both of the above are discontinued. The nut, however, can be replaced by GM #9439915 which is nearly identical.In Appreciation of John Hinckley
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