If you are picky the rivets from cuda junction were a closer match to the original ones from a 1969 St. Louis built B-body, the ECS ones had a smaller outside Diameter on the head, not sure if all plants were the same. Might be hard to tell once it is installed but it was noticeable enough for me to order the cuda junction ones after I got the ones from ECS.
Not trying to bash ECS ether, nothing but good things to say about all their products.

Interesting. The ones I got from ECS when I had to respray the steel dash in my Dad's 69 GTX vert (St. Louis plant) were the exact same size as what was in the car. Maybe it is because his car was an early 69 ? (SPO date of 10/3/68 )

Just checked mine,head size is 0.222,exactly same as my Superbird.I bought what I have from a fellow at the Nationals 15 yrs ago for $.25 ea,he had a couple thousand.

I've got 500 or so from the Windsor plant...I'll check the head diameter.

My original ones measure 0.248 from flat to flat and 0.263-0.267 from point to point.
The ones from ECS measured 0.224 from flat to flat and 0.241 from point to point.
The ones I got from cuda junction are 0.238-0.241 and 0.258-0.259 from point to point.

For reference the original ones are off a 10-24-1968 built car.

The ones that I replaced were on a SPO dated 10/3/68 car from the St. Louis Plant. The ones from ECS were the same size. Who would have thought that I needed to take a pic to show a comparison for something like this on our car for future. lol.

Seems like a lot of fuss over .024 which is about 25/1000 of an inch.

I agree, not much of a difference. Most people may not care and would never notice but some people might like to know.

I am not one of those "if it was that way on my car it had to be that way on every car" kind of guys. I am sure that they didn't spec out the dimensions of the rivets to ±0.001 so I am guessing there are variations out there. Even the two original ones on mine were a little different.

In my case I was repairing a rust spot on the dash and not respraying the vin tag so the smaller head on the ECS rivet stuck out like a sore thumb with the wear marks from the original rivets being visible.

Was there not originally two different length rivets ? Long for padded dashes and short for steel frames ?

What wear marks would there have been on the VIN tag? The only wear marks that I would imagine being there would be from trying to drill it out and the rivet spinning. If that is the case, it could have started wobbling ever so slightly when it was spinning in the hole. That itself could be enough of a variance to give you that .01 difference.

Every tag I have removed from a dash on an A or B-body, has had witness marks from the rivet heads.