Fasst Company Anti-Vibration Inserts (Renthal Twinwall Handlebars) Reduced vibrations felt through the handlebars, which means less fatigue and numbness in arms and hands. High-quality brass inserts with elastomeric expansion joints mounted inside the handlebar. For use with all aluminum handlebars OR Renthal Twinwall bars (not both). Injection-molded plastic endcap along with adapters will fit most counter-bored or countersunk mounted hand guards.