This is an upgrade for the Thing-O-Matic Mk7 Extruder. Features: I created this b/c I was having some issues with the plunger pressure not being adjustable. I didn't want to go with some of the other designs on here b/c of the difficulty of adjusting tension or the difficultly of sourcing exactly the correct springs. Additionally, some of the really nice extruders out there are HUGE! I didn't want to spend hours printing and potentially lose the print on a faulty plunger. For the full troubleshooting story, check out the blog entry, http://slightlynybbled.blogspot.com/2015/09/makerbot-extruder-woes-and-successes.html Additional notes: Things to purchase: Instructions correspond to the order of the pictures. Happy printing!