This is a new and improved drive gear for the upcoming Plastruder MK5. It is backwards compatible with the MK3/MK4 plastruder designs and provides 200% increased push force.For more information, see the blog post: http://blog.makerbot.com/2010/05/21/mk5-drive-gear-now-with-scienceTo purchase one for yourself, visit the MakerBot Store: http://store.makerbot.com/mk5-drive-gear.htmlBolt it onto your extruder and go to town. You will need a new 3/32" spacer to get optimum push force.