Universal seat backrest clamp for aftermarket seats. Required by NHRA for mounting of aftermarket seats. Bolts your seat to a 1 5/8" harness bar. Made from 4130 chromoly and 1018 steel . Tig welded in fixtures. All hardware included. Completely adjustable without removing seat or bracket from car. Designed to clamp to a 1.625" tube. Will NOT bolt to other tubing sizes. Made in the U.S.A!