These things are too cool! Genuine LEGO Rubber 2x4 bricks make great
grippers for Technic or Mindstorm creations (they can also be used as pencil
erasers). They are identical in size to standard LEGO System 2x4 bricks.
The bottom side has 3 holes in the same location as the bottom tubes on
standard bricks. Available in blue, red, and yellow.
(...) Rubber bricks are now located in their own category: Gear>Eraser: (URL) for looking, -Rob Doucette. DoucetteNet LEGO® on BrickLink (22 years ago, 2-Jul-02, to lugnet.market.buy-sell-trade)