The Arduino Mega has four, count them, four mounting holes in a more-or-less rectangular pattern around the edge of the board. Three of the four have enough room for standard pan-head 4-40 screws. The fourth hole is squeezed between two pin-header sockets, to the extent that no screw in my collection will fit.

Screw on Arduino Mega board

Having a lathe, however, makes this situation no big deal… and this time, I put the Sherline drill chuck in the 3-jaw because I wanted to, not because the 3-jaw was stuck. In truth, the lathe chuck simply won’t grab a 4-40 screw at all.

Turning down the screw

I had that pointy right-cutting tool in the holder, so that’s how I cleared off the burr on the backside of the head.

The chuck did grab the hex standoff just fine, though, and the final result looks like this…

Modified standoff and screw for Arduino Mega

For future reference, the turned-down sections are 0.180 inch in diameter; call it 4.5 mm. The snout on the standoff must clear the pins,so it’s 0.100 inch or 2.5 mm long.