I have the upside down mushroom kind that attach by a round shaft that allows it to slide up and down inside a larger diameter shaft which is attached to the blade.  The shaft has a hole drilled in it and you can adjust the shoe height with some large washers by either placing them above or below the sleeve.  (A picture really IS worth a 1000 words!)   Probably clear as mud by I plow a lot of snow on a combination gravel/blacktop/grass and I''m glad I have them.  Saves the grass, saves the blacktop, and allows me to NOT push all the gravel onto the grass!
Also works great for laying a uniform layer of loose material down like sand or gravel.  Just set the shoes to leave a 1inch gap and drive.  Presto - you have a perfect 1 inch layer left behind.  (Can't do that with a box blade although you COULD if it had skid shoes or guage wheels)