Abstract: A resilient spring insert insertable into the separated ends of a chair backrest tubular frame to provide flexible movement of the backrest with respect to the seat. The spring insert is comprised of two carbon steel straps overlying each other and integrally joined together at the ends. Near the ends thereof each strap is bent outwardly in an arch-like manner such that when joined a hollow enclosure is formed. A nylon fastening block with a central hole is placed into the hollow enclosure. The hollow enclosure at each end of the spring insert fits snugly into a severed end of the tubular frame. A fastening screw is passed through a hole in the chair frame and self-threads into the block thereby securing that end of the spring insert to the associated separated frame end.