There is a significantly old mould for part number 3010 (Brick 1x4), which has
a cross-beam support that goes all the way down the central tubes, preventing
hollow stud connections in this area.
This seems like something significant to note, especially considering alternate
numbering exists for other parts with older moulds such as 3003old and 3001old.
Other sites like rebrickable already make note of this difference. I've attached
the distinction they make as an image.
United Kingdom, England
Msg 1 « - cpone