BHJ Harmonic Dampers offer the most precise and advanced execution of the proven elastomer design. Most engine designers prefer elastomer-type dampers because of the durability, their superior high-frequency damping qualities and their ability to dampen all types of vibrations. These SFI approved dampers are all-steel, one piece and are lighter than the OEM units they replace. They have proven their merit in thousands of applications including off shore boats, Grand National stock cars, short track Super Modifieds, Pro Stock and other drag racing cars, Indy cars and street driven grocery getters. All critical OEM mounting dimensions are duplicated for accurate alignment of accessory belts. These balancer feature a TDC mark and are degreed from 0-50 degress in 2-dedgree increments for accurate ignition timing. 90 degree marks are also included for easy valve adjustment. This special SFI approved balancer is recommended for those engines running over 6500 rpm. Installation instructions are included. This balancer is for the 1989-93 Ford Thunderbird SC. They come with a free bolt and washer. You must instal a zero balanced pulley on this unit. If you have any question, take it to a machine shop and find out. take the side of caution.