TFX Pro Packs contain all the parts necessary to find the armature and gearing that best suits your track and driving skills. Each Kit contains one assembled and ready-to-be-oiled TFX chassis with a 16 ohm armature, 15 tooth crown and an installed guide pin. Also included are 18 ohm and 20 ohm armature/gearplate assemblies with idler gears installed and a 19 ohm Rear Axle Assembly. With all three motor and two crown gear options available, all six possible STOCK configurations can be achieved for thorough testing on the track. The complete TFX chassis and the 19 tooth Rear Axle Assembly are both equipped with .352" tires. A set of .360" front tires, .366" rear tires and .378" tires are included to allow the chassis to be raised to handle home plastic or rough tracks. 1-72 and S2-56 flathead screws are included to allow the TFX to mate with any resin or plastic body. Aurora and Model Motoring cars will use the S2-56 screw. AW, JL and resin cast bodies may use either screw depending on their screw hole size. Most racing resin cast bodies will use a 1-72 screw. AW/JL bodies have a hole in between sizes so either screw may fit best. A 1-72 screw will fit most. Two extra guide pins are also included in the kits.