On my 2004 King Cab they were 6.5 inch round speakers. You can easily add a 3/4" thick spacer and install a speaker with more depth than the stock ones.

 

I need to replace my speakers in the doors of 2001 king cab.
Does anyone know what the original size in the doors are ?
They are around 6 inches across.
I would like to replace them with speakers that will fit without having to cut anything. Thanks for your help.

Check out Crutchfield.

 

I need to replace my speakers in the doors of 2001 king cab.

I would like to replace them with speakers that will fit without having to cut anything. Thanks for your help.

These trucks use proprietary-mount speakers in the doors. I have a 1998 and a 2004. I have replaced door speakers in both without cutting, but did drill holes for a sheet metal screws in the metal door area. I used universal 6.5 speakers in both, and I soldered the supplied universal speaker wires to the existing Nissan wires, as the Nissan connectors were also proprietary.

The 1998 had those little nubs on the 1998 which hindered using aftermarket speakers unless the nub was cut off or a corresponding hole was drilled in the speaker frame.

Anyway, for the 2004 the 6.5 inch speakers would fit and not hit the window when down if I drilled four holes four mounting with sheet-metal screws supplied with the speakers. I also stripped the speaker wires a little (without cutting) and spliced in the wires supplied. Then I pushed the wire harness to the inside part of the door, and connected everything up.

I need to add that one needs to be careful taking the door panels off, especially the rectangular trim piece, like Step #1 (Pry up on the FRONT edge of it. No need to remove screw securing door pull handle). Also, the Nissan speaker mounts are proprietary so I had to choose whether to cut off a locating "nub" or drill a corresponding hole in the new speaker frame so it would sit flat. There may be adapters available from sources like Crutchfield.

Also, the wire connections are proprietary as well. I used the wires that came with the aftermarket speakers and simply used solder/shrink tubing to attach those to the Nissan wires. Again, maybe Crutchfield has a plug in adapter kit for this.

 

These trucks use proprietary-mount speakers in the doors. I have a 1998 and a 2004. I have replaced door speakers in both without cutting, but did drill holes for a sheet metal screws in the metal door area. I used universal 6.5 speakers in both, and I soldered the supplied universal speaker wires to the existing Nissan wires, as the Nissan connectors were also proprietary.

The 1998 had those little nubs on the 1998 which hindered using aftermarket speakers unless the nub was cut off or a corresponding hole was drilled in the speaker frame.

Anyway, for the 2004 the 6.5 inch speakers would fit and not hit the window when down if I drilled four holes four mounting with sheet-metal screws supplied with the speakers. I also stripped the speaker wires a little (without cutting) and spliced in the wires supplied. Then I pushed the wire harness to the inside part of the door, and connected everything up.

I need to add that one needs to be careful taking the door panels off, especially the rectangular trim piece, like Step #1 (Pry up on the FRONT edge of it. No need to remove screw securing door pull handle). Also, the Nissan speaker mounts are proprietary so I had to choose whether to cut off a locating "nub" or drill a corresponding hole in the new speaker frame so it would sit flat. There may be adapters available from sources like Crutchfield.

Also, the wire connections are proprietary as well. I used the wires that came with the aftermarket speakers and simply used solder/shrink tubing to attach those to the Nissan wires. Again, maybe Crutchfield has a plug in adapter kit for this.

Thanks for the Great info.