Q: Must I use the OPC-2401 with a PTT switch in order to key the microphone on my headset? If I simply push the PTT on my IC-A16 while my headset is plugged into the adapter, does it key the microphone on the headset or the microphone on the IC-A16, or both?

A: You do not have to use an external PTT switch with the OPC-2401.
If you just plug in your headset and use the OPC-2401, pressing the PTT on the IC-A16 will activate your headset's microphone. The radio's internal microphone will be bypassed.

Q: will this work with the ICOM-a14 hand radio

A: No, it will not.  For the IC-A14 you will want the Icom OPC-499 headset adapter found here.

Q: This Icom OPC-2401 headset adapter for IC-A16 works with BOSE A20?

A: Yes, this will work with the Bose A20 - General Aviation Dual Plugs. 

Q: Will this work with the ICOM- A6 hand radio

A: No.  For the Icom IC-A6 you would want the Icom OPC-499 replacement headset adapter.

Q: What head set or ear piece can i use with this adapter. I just purchased the Icom IC A-16.

A: This works with IC-A16 transceiver and any standard dual plug aviation headset.