These pieces are the same size and shape as the common black pieces that are used as the head top pieces of the robot action figures (shown in the photos for reference, not included).  They are also used in a number of specialty applications such as flashlight lenses, headlights and taillights for vehicles, or the snake eyes in the Screamin' Serpent Roller Coaster.  Two of them placed together on a rod can also be used as small wheels.

You will receive 20 Yellow pieces and 2 Light Red/Pink pieces with each lot purchase.

Buy from us with confidence! I am a lifelong avid K'NEX builder.  I know the parts well and have a huge selection.  Please feel free to contact us with any questions, or if we can be of any help finding a specific part for you.  I would be happy to put together bulk lots of any part and quantity that we have available.  Thanks for looking!