One Pair 12" x 2" Electric And Hydraulic Brake Package Include 1 Left and 1 Right 12" x 2" Trailer Electric Brake Assembly Electric Trailer Brake Assemblies Fit Most 5200lbs 6000lbs 7000lbs Trailer Axles Bolt on Application to Standard 5 Hole Pattern Center Hole Diameter: 3-1/4" Bolt Hole Spacing: 2.0" O.C. Around the Top Bolt Hole Spacing: 3.0" O.C. Across the Bottom Center Hole Diameter: 3.25" Inches Fits the wheel bolt pattern 6 lug or 8 lug, fits spline size 42 steel drum These are fully assembled backing plates with shoes, springs, and magnets attached and ready to be mounted