What’s the difference? I’ve always thought of an elevator to be something like this: http://www.fourwinds.net/ebridle/bimg/WB130058.jpg
But I’ve also seen certain bits that I consider gags (Dutch gag/3 ring bit or the American gag like this http://www.horsetackinternational.com/images/F5087-gag-bit.jpg) called “elevators.” I always thought of a gag as a bit that raised up into the lips when the reins were pulled. So what’s the definition of an elevator? Or are there some overlaps between the two?