Pro Series Trotter The Pro Series slat mills are our top of the line Treadmills. They have everything you need to put a dog in top notch physical condition. All Pro Series mills include the following: All Aluminum Frame. Accubrake. 12 Function Digital Speedometer Anti Skid Composite Slat Trck 8" Dolly Wheels. Sealed Precision Free spinning bearings. Heavy Duty Axles and bearing setup with 1 25" aluminum axles. Fully adjustable tracking system. Fully adjustable tethering system. Backed by our two year axle to axle warranty.   About Size