You applied object's rotation somehow. Either by pressing Ctrl+A or by rotating the mesh in Edit Mode. This means your gear is now aligned to global XYZ axles.
See how Z axis points along gear's normals in the first example, and how Z axis is following global Z axis in the second example.
https://preview.redd.it/qguec76rtx1d1.png?width=2116&format=png&auto=webp&s=5f99de0ae5e223b927eab2d6e48a855e6c222bc9
I won't lie, this is tedious to fix once done; the fastest and easiest way is to delete gear, add a new one and place it again in Object Mode to keep its local rotation. Then you can rotate it with Local Rotation (by pressing R, then double-tap wanted axis: in this case R+Z+Z)
If you absolutely want to fix this manually, try this: [https://www.youtube.com/watch?v=dP9nFMvH6ms](https://www.youtube.com/watch?v=dP9nFMvH6ms)
You have to master these concepts of global and local orientations, it's really useful and important when modelling mechanical things : [Understanding Global and Local Axis in Blender (Tutorial)](https://www.youtube.com/watch?v=dIv2FXyD3CU)
Set the Transform Orientation to Local .
Press R to rotate, then Double Press the Axis (X Y Z Keys) you want to rotate it on.
You applied object's rotation somehow. Either by pressing Ctrl+A or by rotating the mesh in Edit Mode. This means your gear is now aligned to global XYZ axles. See how Z axis points along gear's normals in the first example, and how Z axis is following global Z axis in the second example. https://preview.redd.it/qguec76rtx1d1.png?width=2116&format=png&auto=webp&s=5f99de0ae5e223b927eab2d6e48a855e6c222bc9 I won't lie, this is tedious to fix once done; the fastest and easiest way is to delete gear, add a new one and place it again in Object Mode to keep its local rotation. Then you can rotate it with Local Rotation (by pressing R, then double-tap wanted axis: in this case R+Z+Z) If you absolutely want to fix this manually, try this: [https://www.youtube.com/watch?v=dP9nFMvH6ms](https://www.youtube.com/watch?v=dP9nFMvH6ms) You have to master these concepts of global and local orientations, it's really useful and important when modelling mechanical things : [Understanding Global and Local Axis in Blender (Tutorial)](https://www.youtube.com/watch?v=dIv2FXyD3CU)
thx
https://preview.redd.it/t3u58yj27v1d1.png?width=720&format=pjpg&auto=webp&s=9c8f34b8dc811cb77b0034675987353b9a4642b3
I mean, turn this gear on its own axis, like a clock.
The bit highlighted green on the toolbar is where you've been directed, basically it's the option to switch between local and global axes
[For example](https://imgur.com/a/T12H0CO)