Copying key frames?

Is it possible to copy and paste (per say) key frames? Like if i was animating a fan or tire, to where i wouldn’t have to make every single key frame for it?

You can copy and paste key frames in the NLA editor, but it would be a lot easier in either mentioned scenarios to just insert the key frames for 1 cycle in a loop (IE 1 full rotation of the fan blades), then go to the IPO curve editor, select the rotation curve in question, then go to “Curve” -> “Extend mode” then select “extrapolation”. If you do that, the fan will spin endlessly through your animation.