Not compatible with the SHK-1 Full Brim. For Full Brim Compatibility check out Universal Ear Defender The STUDSON Ear Defender gives reliable, helmet-mounted hearing protection for loud jobsite environments. It clips straight into the side rails of the SHK-1 Cap Style helmet and delivers solid noise reduction without getting in the way of your work. Key Features Clear CompatibilityMade primarily for the SHK-1 Cap Style helmet (vented or non-vented). Secure 30mm MountingUses a standard 30mm attachment that locks into the SHK-1 Cap Style side rail for a stable, low-profile fit. Noise Reduction Rating (NRR)Rated at 24 dB NRR and tested to ANSI S3.19-1974 noise reduction standards. Easy On/OffSnaps on quickly when you need hearing protection and swings up out of the way when you don’t. All-Day FitAdjustable ear cups create a snug, comfortable seal that stays put through long shifts.