Just passing this info on for those that may need it.
noticed that one of my HF drivers was a little loose and needed to be re-tightened to the horn. Well, I found out it wasn't exactly what I was used to, which was to take the whole horn assy out the box and tighten the driver from the rear. Upon closer inspection I realized the bolts were at the front of the horn and covered by a black oval piece of adhesive paper, that hides a hex bolt. I have a bunch of allen wrenches around the house and NONE of them fit.....aaggggghhh! Picked up a 10 piece set of SAE and 10 piece metric (just in case) from Lowes for about $4 each.
The size is 3/16th.