Phew - lots of questions here.

Lets start with timeline stuff.

I (John Pasemann from US Car Tool, manufacturer of the Laser Cut Frame Rail Connectors) got an email from David (purchaser) he sent on Friday evening. I read it at home on Sunday evening. David mentioned his recently received frame rails did not seem to fit. I asked for a picture and Monday AM checked his picture against the CAD drawings of the connectors and sure enough; we had sent him the Challenger set although he had order a Cuda set.

I issued an RMA number for the return, processed the return shipping label from him, emailed it to him (no cost to David) and processed an order of a Cuda set of connectors that left here today.

So I think we are golden on the customer service bit, except that we made a mistake in shipping the wrong connectors to begin with.

Now, about the technicalities of various floor pan differences.

There are 5 different versions of frame connectors at the moment.
1) Dodge E Bodies (Challenger)
2) Plymouth E Bodies (Cuda)
3) Dodge & Plymouth B Bodies 66-70
4) A Bodies 67-69
5) A Bodies 70-75

The wheelbase differences between Dodge & Plymouth on the A & B bodies are accomodated by the amount of overhang on the rear frame rails and the same connector will work for both. This was no accident and a lot of design engineering and trial fitments went into having one part that accomodates both wheel bases.

This was just not possible on the E bodies as the rear frame rails are angled and the variation in wheelbase along with the angled rear frame rails requires crossing the "terrain" of the floor pan in a different location - hence the need of unique connectors for Challengers and Cudas.

And now on to the technical issue of strength.

I think we need to be careful using terms like thin wall and thick wall. The US Car Tool frame connectors are made of 1/8" thick steel (.125 or 125 thousandths) so what thickness is the "thickwall tubing" vs thinwall being referred to?

This was discussed at length in the past, but to boil it down, the strength of the frame connector comes more from the "structure" that is formed when it is welded to the floor than from the thickness of the sidewalls of the material. One of the reasons the US Car tool frame connectors are effective is how they tie the entire floor (a part of the unibody structure and also a shear plane) into the frame connector and form a structure that is (roughly - depending on application) a 2 x 4 Rectangle structure.

One measure of this "strength" is referred to as the modulus of elasticity. I'll bet there is an engineer on here who is willing to do the calculations and compare the section modulus for a 2x2 x .250 (quarter inch) sidewall tube vs a 2x3 x .125 (eigth inch) sidewall tube.

That should answer some questions, cause a few others and in general stir the pot a bit (chuckle).

Hope that helps, as always - MOPARTS ROCKS!