Weatherproof Bass Blockers for 3.5 3 1/2 Inch Installer 3 Pack Installer Jobber 3 Pack Guaranteed +/- 10% Tolerance, Weatherproof Axial Leads, Non-Polar 10% Capacitor Blocks Sounds Below 2.8kHz (14 mfd @ 4 ohm), Reduces the drive signal 3.5" 3 1/2" Speaker Size Recommended although can be used for any application. The speaker size is our recommendation please be sure you want to block sounds below 2.8kHz.