What is this black brick with red tubes inside? In an old plastic bag with heterogeneous Lego bricks, I found three or four like this.


I can't recognise them: does anybody know what they are? In which set(s) were they used? What for?

A few more details. The small red tubes sound like they are slightly loose inside the brick. The one that connects the long sides is unobstructed (while of course it interrupts the other two).
From above, the brick looks like normal 2×4 black one, apart for the holes on the sides:
This is a 7049b - Wheel brick. It was used with the first LEGO wheels back in the 60's to create vehicles like this:



This was a very common piece (in white and black) when it was produced between 1959-1992 and was used in 176 sets according to BrickLink.

Per @GalacticCowboy's comment: As shown in the inset, the wheels had a metallic axle that snapped into the holes. Because they were modular, you could use wheels in whatever configuration you desired.