CUSTOM MADE Aftermarket 4" Voice Coil. - 3.965" I.D. on black anodized aluminum former. Compatible with Rockford Fosgate T212D4, T215D4, Punch HX2 RFD3118, Power RFR3110, Power RFR 3112, Power RFR3115 and others with the 4" voice coil, as well as many other subs that require the specs above.