I've been working on a little history project to make a shadowbox/display-type thing of all of the major evolutions of the 2x4 brick over the years. (I know this can get really in-depth, and I'm trying to hit major changes only, to preserve my sanity).
My question is this: is there such a thing as a 2x4 brick (it would be ABS) with the "Pat Pend" obscured (covered by a blob, denoting an updated mold), that has tubes only?
In other words--no braces, horizontal crossbars, ridges of any kind (no slotted tubes either), just like a 60's brick, but made late enough to have the "Pat Pending" obscured, but early enough to not have any added reinforcements.
Also, by all of this I mean a brick that would have been in normal sets, and not a sample or test brick.
It's getting frustrating, and I wonder if I have invented this category!