I'm working on the front suspension and steering components of my 74 Road Runner and decided to replace the idler arm bolt because it got sand blasted a little too hard. I found one on a 74 Charger and it has a different nut. Both nuts are the self locking variety where the nut itself is squeezed a bit in one direction, however they are very different in appearance. This led me to the parts book and it shows a bolt with a castle nut and cotter pin. Neither of the bolts I have are drilled for a cotter pin and the nuts are definitely not castle nuts. I likely changed the idler arm on my Runner in 78 or 79 when I put the old DC headers on and the stock idler interfered, but knowing myself I would have most likely reused the original bolt and nut. What is everyone else's experiences with the idler arm bolts on the 73-74's???

That 74 Charger one looks like it has a nut off a Power Steering Pulley.

I've never seen a castle nut on the K-member thru bolt. My guess is that it's a misprint in the manual and it should go to the nut on the centerlink.

Run the Charger bolt with a new locking nut. IIRC, Moog usually give you a new locking nut with a new idler. It's all good.

70-72 E-bodies used a castle nut and cotter pin for the idler arm. My early built 73 also used that style bolt. 73-74 used the style in your picture. That is what the fastener guide says anyway.

Hey Burdar, does the fastener guide indicate which nut style - tall, short, or both, was used? Both styles are available in the 74 parts book in the standard parts section.
I have seen an e-bag sale which included the shorter nut. I'd like to pin down the nut style originally used. Perhaps the short nut style is a replacement from Moog, perhaps not, I don't know.

This is from the E-body fastener guide...

Bolt: 73 and 74 9/16-18 x 3.62"

Nut: 9/16-18 self-locking .53" thick

Thanks for all the responses. I measured the two nuts and the larger one from my Road Runner is 0.53". I'll go with it.
Now... I assume it was originally phosphate black???

yes