Hi I am fairly new to making music and MIDI.

I am building a MIDI device that uses an Arduino Mega as the processor, a powered USB hub to connect USB MIDI devices and MIDI DIN sockets to connect the whole thing to multiple synths.

I am using the schematic found here as the basic foundation:
https://www.arduino.cc/en/Tutorial/Midi

I have connected four USB MIDI devices to one synth already by breadboarding the project. I am moving on to a more permanent device to be able to connect to multiple synths using the schematic provided.

The MIDI sockets I am using are similar to the one found at the link below:
https://www.adafruit.com/product/1134

The housing connection on a panel mount MIDI socket can be seen here:
http://www.hobbytronics.co.uk/5-pin-din-chassis-socket

The above is just to be thorough. My question is regarding the connection on the sockets that connects to the circular MIDI cable housing that inserts into the socket. This is the part on all MIDI cables that has the dimple to let you know how to insert the MIDI cable. On the socket itself, there is a tab available that allows a connection to be made to the circular cable housing. It appears that this is not connected on synths in a way that would allow a continuity tester on a DMM to test positive.

How is this connection on the socket supposed to be used?

I have used a DMM on a MIDI cable plugged into a Korg volca fm to see if pin 2 on the MIDI cable is connected to the MIDI cable's circular housing. There is no direct connection.

A further question is is it safe to not connect this point to anything in an electronic device?

Thank you.

Personally, I would think that this point would be connected to the same connection as pin 2 on the socket - to ground. My device works but I am trying to be thorough.