Fibre-Metal® By Honeywell 2029 Noisegard® Quick-Slot™ Hearing Protective Muffs with 25 dB NRR are compatible with Fibre-Metal® and other non-slotted caps. Muffs require no tools to install wherein dielectric ratings is not distressed and accommodates easily on most hard hats as well as caps. Muffs with quick-slots allow easy attachment to non-slotted caps and can be detached for slotted caps. Quick-Slots allow ear muffs to attach to non-slotted caps. Quick-Slots can be removed for slotted caps. No tools are needed for installation. Fits easily on most hard hats and caps. Noise Reduction Rating (NRR): 25 dB.