overblows and overblow bends

Great, glad I asked.

Draw bending happens on holes 1 through 6 on the harmonica. Blow bending happens on holes 7 through 10. There is no difference in approach from draw bending to blow bending. You'll of course be using more of the front of your tongue, further forward in your mouth due to the fact that these are high-pitched bends.

With a standard (draw or blow) bend you're activating the other reed in the slot a half step above it's natural vibrating pitch. For example... if you play 4 draw bend on a C Harmonica, the 4+ reed, which is normally C, will vibrate somewhere around Db, a half step above what it's tuned to. Another example... if you play 8 blow bend, the 8 draw reed, which is normally D, will vibrate somewhere around Eb, a half step above what it's tuned to. In standard bending, which both of these examples are, the pitch will slide smoothly downwards from the reed you're playing to the reed it's transferring to.

This is all covered in Bending Study 1 and MRI paper I wrote... review both of those. Blow bending is specifically covered in Bending Study 6.

Overbending works with the same principle, but you will not hear a slide in pitch. When your mouth is tuned to the correct pitch, the other reed will sound. Note that with overbends the pitch goes up when you bend. Overbends are taught in Bending Study 7.