Gar, they are 5/8" drywall screws, they worked out very nicely. I had some #8 stainless screws with some washer ready to go but when I discovered how little space there is between the screw and hole I had to go with something less stressing on the wood. I predrilled and torqued the screws down with the lowest setting on my drill...it worked out nicely. (shame on Eminence BTW!)
Also I got two different looking H290 horns in that one must be a new rev. because its hole could have been much smaller...probably at least an inch smaller both ways.I think i'll take the stainless screws out of the Omegas and replace them with black screws as well...I am fortunate to have a hardware store nearby with an insane selection of screws and they have some #8 black screws.