Add a new seat to your Knex roller coaster and give your toys a ride! We created this new seat to thrill Playbmobil kids on the Knex coaster.Created with Blender, sliced with Slic3r, printed on a Printrbot Jr. Print upright with support material. To install, remove the two screws on the back half of the Knex coaster car. The two cylinders on the bottom of the seat will match the holes. You'll need to use two different screws with sharp points to dig into the plastic. Use a rubber band as a seatbelt by slipping it through the holes and attaching to the T on the back of the seat.