This chassis is designed to replace the tubular chassis that comes with the Pitsco HD50073 Solar Designer Kit. The original chassis requires drilling axle holes through an extruded plastic tube that flexes during drilling. This made the car run crooked unless the hole was perfect. The motor would also fall out unless taped in, and the solar cell also needed taping. The gear engagement was often too tight with the original taped motor mount. I previously uploaded a printed motor clamp to fix the motor problems, but decided to do the whole chassis. Axles-true; Motor- secure; Gears-perfect; Solar Cell-secure