Pro version features metal hardware. Dial and lock in your sound settings with D Addario s easy-to-install Loknob. Once in place, simply rotate the knob to click into the sound you need. For larger sound adjustments, lift the knob, rotate to your desired sound, then release. Loknob retrofits to most foot effects, studio effects, and mixers. MFSKU PW-LNPS-01B UPC 019954307417