These Zippy spacers are custom-designed for the Hansen Metals Solo butterfly knife They add positive jimping to the Solofor extra grip, and include a tungsten weight system for adjustable balance. This allows you to add end-weight to the Solo to add a light to moderate handle bias.
My personal preferred SuperFly balance is with inlays + spacers (no tungsten weights installed). This configuration weighs 4.64 oz total.