The M2.5 Standoffs (Spacers) arrived in the mail yesterday. The original standoffs that I ordered were M2 or 2 mm size. The Raspberry Pi board has holds for standoffs that are 2.75 mm in diameter. No M2.5 standoffs showed up in my initial Internet search for parts. Wasted time and money, mostly money on the order of $10.00.
As I mentioned in a previous blog post, the M2 would have worked on the Raspberry Pi but were too narrow for my holes that I drilled int the third and topmost platform on the robotic car. The holes that I drilled were for M3 standoffs and were 3.2 mm in diameter. One of the M2 standoffs fell through the hole. The M2 would work if they were carefully tightened against one side of the hole. That did not seem secure enough for my comfort though it probably would not have been a problem.
The M2.5 Standoffs were specifically marketed as being for Raspberry Pi boards. In the wee hours of this morning, I replaced the brass M2s with white plastic M2.5s. The M2.5 standoffs fit so much better. The diameters of the nut and shaft of the M2.5 standoffs are larger than my 3.2 mm holes. The plastic screws fit nicely on the Raspberry Pi Board.
I also decided to go with longer standoffs when I made the change. The M2.5 standoffs are 3/4 of an inch. This raises the Raspberry Pi board completely above the Arduino and its Motor Driver Shield.