Just a classic Playskool rainbow colored stacker--an icon of good design as well as an engaging and pretty much indestructible toy for the kids.  The fact that a few different companies produced these, each a little different (and Playskool itself has produced several versions) makes them a great thing to collect and display as a group, too. 

9 1/4" t x 3 5/8" widest diameter. Excellent condition, with just the right amount of wear; colors still nice and bright. The post on this one is not threaded but just sticks into the base, tight and flush.