Single pin connector - speaker mike
The single pin connector style appears to be the easiest to use for a hand-held scanner. I've had to cut through a two pin style and it's a bit of a hassle. As to pin diameter, if an adaptor is needed, one should be available at a Radio Shack or other place that sells audio equipment and accessories.
The single pin style obviously carries both audio out and voice in. To me it seems logical that it should carry audio from the scanner just fine. No way to know for sure without trying it out.
Please note that the audio output jack on a hand-held scanner has a component inside (resistor I suspect), that limits the audio level for use w/ head phones. Lawyers didn't think the user would have enough sense to keep the volume at a safe level. So....the audio doesn't peak out like you might expect. But since the speaker is close to your ear, you should be ok.
Take care,
Julian