The short bolt in the LIC kit is a zinc plated, Grade 5, hex head bolt, with a TR headmark. It is 1” long, and has 3/8”-16 (coarse) threads. My confusion started because the nuts used for the two idler arm bolts are given as GM #9422298 in the 1966 AIM. That nut was used for both upper and lower idler bolts from 1966 until 1982. I knew that the GM nut has 3/8”-24, or fine threads. Which means the two idler arm bolts that GM originally used also had fine threads. After additional research I learned that the upper idler arm bolt listed in the ‘63 through ‘67 AIMs, and used until 1982 was GM #181365. That bolt was never available as a service replacement part. It is a production-only part. It was never possible to purchase that bolt from GM, so you will never find an NOS example. In any case, that bolt is known to have 3/8”-24 (fine threads) and that bolt had a very dark, plain finish.

Now a bit more about the nut (GM #9422298) used for the two idlers arm bolts from 1966 through 1982. That nut was a locking nut, sometimes called a prevailing torque nut. It was Grade 8 and was zinc plated. That nut was GM-discontinued many years ago, but the second image shows an NOS example of that locking nut. Note the six dots on the top side of the nut, indicating Gr. 8. (Some GM suppliers of that era designated the same Gr 8 locking nut with six dimples.) Also note the three trapezoidal indentations.

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Now let’s return to the LIC reproduction bolt and nut kit in Image #1. First, both bolts and both nuts have 3/8”-16 (coarse) threads. Which we know is incorrect. Second, the short bolt is zinc plated. That also is incorrect. Third, the locking nuts are Gr. 5, whereas the GM locking nuts were Gr 8. Other than the finish on the long bolt, there is not much that is “NCRS-correct” about the LIC idler arm bolt and nut kit. The idler arm bolt and nut kit from Corvette Central is identical to the LIC kit. The idler arm bolt and nut kit from Paragon is only slightly better, in that both bolts in the Paragon kit are dark, probably black phosphate. But the bolts and nuts in the Paragon kit also have the incorrect coarse threads. And the Paragon locking nut is Gr. 5, not Gr. 8. Obviously, the Corvette reproduction parts companies are not able to provide correct idler arm bolts and nuts for people who care about appearances and NCRS judging.

Faced with the many inaccuracies with the reproduction idler arm bolt and nut kits from the various catalog companies, I set out to find the closets nuts and bolts I could find to correct. Here’s what I’ve come up with: I found a version of the short bolt, with the critically important feature that it has a period-correct TR headmark. It is 1” long, with 3/8-24 threads, and with a very dark finish, consistent with the original GM bolt. I also found a source for Gr. 8, zinc plated locking nuts with 3/8-24, fine threads that are a very close match to the GM-discontinued 9422298 locking nut.

I also found a source for a Gr. 8, zinc plated locking nut with coarse threads for the reproduction carriage bolt. Now I’ve already told you that coarse threads are not correct for the carriage bolt, but I know if no source for a correct version of the lower carriage bolt with 3/8-24, fine threads. So, the best that can be done at this point is to use a 3/8-16, Gr 8, locking nut that looks nearly identical to GM-discontinued 9422298, except having coarse instead of fine threads. For 66-82 cars, my kit includes a fine-thread, Gr 8, dark finish short bolt with TR headmark, with a companion Gr. 8 zinc, fine-thread, locking nut, and also a Gr. 8 zinc, coarse-thread locking nut for the repro carriage bolt. Cost is $14, plus $5 shipping. My kit tor 1966-1982 is shown in the next image.

For owners of 63-65 cars, the situation is slightly different. For those 3 years, regular hex nuts and lock washers (dark plain, unplated) were used instead of locking nuts. For the upper, short, idler arm bolt, I can provide a black phosphate lock washer and a 3/8-24 hex nut in Gr 8, black phosphate. These black phosphate fasteners look nearly identical to the original, unplanted nuts and lock washers that GM used. Let me know if you have a 63-65 and I will include regular lock washers and a 3/8-24 (fine) regular hex nut instead of the locking nuts. At present I do not have a source for a 3/8-16 (coarse) hex nut in dark plain or black phosphate, so you will have to find such a nut on your own if you are using the repro, coarse thread, long carriage bolt on 63-65 cars. Cost is $14, plus $6 shipping.

I am still hoping that someone will eventually reproduce a correct, fine thread carriage bolt, but for now we all have to settle for replacing the upper bolt and its locking nut (for 66-82), and the lower locking nut (for 66-82). That is as close as we can get and in all likelihood if you use my kit, you will get no deduct during NCRS judging.