What is this old wheel brick? Wheels are also available in about the half size. They have metal axles.
There are some variants registered on bricklink, but judging by the name and the presence of the brick in the middle, I guess the closest is: Wheel with 12 Studs and Axle Cam with Light Gray Tire Smooth - Large (715a / 36)
The small version you mention is probably: Wheel with 4 Studs and Axle Cam with Light Gray Tire Smooth - Small (7039b / 132-old)
Henrik covered wheels, so I'll just mention the brick used to attach these - Brick, Modified 2 x 4 with Wheels Holder, Trans-Clear Bottom
As noted on Bricklink there could be some variations of this brick:
Several versions of this brick exist. Bush colors have been reported as red, black, milky white, and mixed colors, as well as a version missing the middle bush.