CAS331-4000 / 331-4000 EARMUFF MODEL 4000 20EA/CA Model 4000 Earmuff The Model 4000 Earmuff provides exceptional attenuation and outstanding comfort, yet its one of the lowest priced earmuffs in the industry. Vertical adjustment system and large ear cup openings provide a custom fit. Lightweight design and soft, wide cushions ensure even pressure and superior comfort. NRR 27.