These Zippy spacers designed for the BBbarfly SuperFly balisong trainer are made in-house from a rubbery, shatter-proof polyurethane. They add positive jimping to the SuperFly for extra grip, and include a tungsten weight system for adjustable balance.
My personal preferred SuperFly balance is with inlays + spacers (no tungsten weights installed). This configuration weighs 4.33 oz total.