Photoshop : Screw heads

Step 1
Make a circular selection.
Tip: Hold down Alt/Option to draw from the center. Hold down Shift to draw a perfect circle. To move the selection while drawing, hold the spacebar.

Step 2
Select the gradient tool. black to white circular gradient. Make sure you check the reverse box on the top bar.

Step 3
draw the gradient starting from the center and you should have something like this.

Step 4
Now how about the slot?
Make a new layer. Draw a long rectangle and fill with dark gray.
To trim the slot: Ctrl/Cmd click on the layer 1 thumbnail to select it. With the top layer active hit Ctrl/Cmd+Shift+I to invert the selection. Press the delete key. Now you should have a nicely trimmed slot.

Step5
To make the slot look recessed:
Add a layer style to the slot. Hit the little "f" at the bottom of the layers pallette. Use inner shadow wih the default settings except for the size, move that up a little bit for more realism.
Step6

We are done, but how often is the slot perfectly vertical? Press Ctrl/Cmd+T for free transform. Move your mouse on a corner until it turns into a curved arrow. Drag it around until you have a nice angled slot.

Final