Hagstrom guitar catalogue. Page 2. Description of the Hagstrom H expander-stretcher neck insert that allows Hagstrom's famously low action. This truss rod insert was very much the selling point for Hagstrom guitars in the mid-1960s, with two pages (p2-p3) dedicated to the design in the previous US Hagstrom catalog. The design was naturally patented, with the number 190125.