Does the DV500 tripod plate fit an HD100?
 

The model number is KA-510u. I can get a good deal on a used one.

A tripod mount is a tripod mount, right? Any reason this won't work on an HD 100?

I don't think so
 

I own the DV500, DV5100, and HD200. The 500 has a different plate then everything else. Not sure why they did that. The 5100 and the 200 are the same. And I believe the 200 is the same as the other HD models.

Thanks! Glad I posted... that saves me a lot of trouble. I wouldn't have guessed that.

confirmed. You can use Sony's tripd plate on the GY-HD/HM series the GY-DV500 had the odd (but similar looking) plate.

OK, is it possible to take the plate from the GY-DV5000/5100 to the GY-HM700?
Does is fit?

Yes. It should.

The wedge plate from a 'standard' camera will fit the mounting holes in the 500, so you can attach the 500 to the same plate as the 5000 series and other pro cameras. Be aware that the rear pin is NOT in quite the correct place, and although it does nearly align, it will not make full contact. However, my 500 on a tripod is perfectly safe and shows no signs of coming detached. Having a non-standard plate was far too annoying.