Harmonic Balancer Small block Fits Chevy stock-type replacement 6-3/4" diameter harmonic balancer. For internal balance engines. NOT recommended for RPMs in excess of 6500. NOT SFI certified. Internal balance. Balancer Bolt Spectre’s Harmonic Balancer Bolt Kit is designed to fit Fits Chevrolet Small Block 265-400 Fits V8 engines. This grade 8 bolt is 2-1/2 inches long, and features a plated finish for corrosion resistance. This kit also includes a security lock washer.