The Black and Blue Phaser Ones
But we know that it did fire on other settings for we "saw" it do it.
These mechanical facts have been right in front of us for so many years. If you have the old paperback book "The Making of Star Trek" with those poor old black and white photographs in it, take a second look at the open phaser one. You can make out the knob, the link to the Plexiglas and the battery holder.
One final "urban myth" to clear up: the trigger or knob on the bottom of the phaser one.
There was a small raised round aluminum button/rod there on some models. No one knows why it's there. A mock trigger? A knob to help hold on to the phaser one? (Very likely, as the little darlings were slippery) Or simply a knob to help remove the bottom when servicing it? Who knows?
The non-working models of both the pistol and hand phasers were mostly cruder than the above described. They had poor detailing, that is, when detailing was even remembered, and misshapen bodies, Velcro-glued for "invisible" holsters, etc.
Funny thing, I have seen a very clean copy of the phaser one with a fixed raised plate mounted on it. Why? Maybe for a close-up model.
Well, that's it, every detail known to human and Vulcan on the history of the black and white classic phaser.