Our 1973-1979 GMC Truck dual dash mount speaker consists of two, Custom Autosound 3.5" speakers that are mounted on a board to give you stereo sound from the original, mono location. This 1973-1979 GMC Truck dual dash mount speaker is designed to act like your original 4x10 speaker, but provide better sound. It mounts to the original 4x10 studs in your dash without the need for any extra brackets. The 1973-1979 GMC Truck dual dash mount speaker has two, 4 ohm speakers and is designed to work with our modern, replacement radios. If you have an original 8 or 10 ohm radio, you may still use this speaker, but you will have to wire it in series and may or may not have to add an inline resistor. Please be careful when using with an original mono radio as improper wiring may fry your original, 8 or 10 ohm radio.