Feature●5 of our most popular see-through marble run pieces allow you to see all the action.●2 - Y splitters alternate moving the marbles in two different directions (this is one of our most requested pieces).●Standard toy size marbles (5/8 inch or smaller) work with this set (no marbles included with this set).●Compatible with Marbulous Marble Run Toys including our Marble Genius Marble Run Starter Set (60 pc.), Super Set (85 pc.), Extreme Set (125 pc.), & 8 Accessory Sets.Description