3/8-16 Cadmium Plated Hex Nuts

After a very challenging search I found a source for cadmium plated, 3/8-16 hex nuts. These nuts are 3/8”-16 x 0.324” thick (21/64”); 9/16” AF. This is what these nuts look like.

These nuts have a professional quality, bright finish, not a dull finish, which some people expect, but which can, and often does, indicate a degradation of the plating or a non-professional, home plating.

This is the label with the cad plating specification on the bag from the original vendor.

These nuts are equivalent to GM 120377 which were used throughout the C1 and C2 Corvette era. The 120377 part number dates back to at least the early 1950s, and quite possibly into the 1940s. So, it’s a very old GM part number, as a six-digit part number would suggest. GM 120377 is one of very few fasteners on C2s that were cadmium plated, rather than zinc plated. As you probably know, cad plating is more expensive than zinc plating and it’s much more durable and resistant to oxidation and corrosion than is zinc plating. That must be the reason that GM specified cad plated nuts at certain locations, especially underbody locations exposed to water, debris, exhaust fumes, etc.

My particular interest in these nuts is because I own a ’66 that I’m restoring and I’m using these nuts on my car. For ’66, these is a minimum of 6 of these nuts on all cars, but as many as 15 of these nuts were used on cars with specific options, including: C60 (AC), K19 (A.I.R.), N03 (36-gallon fuel tank), and N40 (Power Steering). It’s up to you to know how many of these nuts you need for your specific car. Check your ’66 Assembly Instruction Manual if you’re unsure where they go. When 120377 was GM-discontinued, probably in the 1970s, it was replaced by GM 9414034, which is GM grade 301M (SAE Grade 8) nut, which is zinc plated with a yellow/gold dichromate over-finish. Of course, a dichromate finish on bolts and nuts is completely incorrect for C1 and C2 Corvettes.

I’m selling these for $0.75 per nut, with a minimum order of 6, plus $6.50 shipping to US destinations only. That makes a grand total of $11 for 6 nuts. The shipping cost may be slightly higher if you buy 10 or more.