Guys, we're going to be laying hardwood in most of our house including the stairs.

The stairs will be fitted with NuStair treads (5/8" thick with nosing/scotia pre-glued on)
http://www.nustair.com/specs.aspx

Our supplier suggested that we can use 6 finishing nails per tread, without glue & not have any squeaking issues down the road since that's how his business does it. (The NuStair site says glue and nails.)

*IF* we did that (nails only), would you guys shoot 15 ga finishing nails at angles, or would 16 ga be sufficient?

IF we used glue & nails, would 16 ga suffice?

Do you have any other ideas?

The stairs are closed, no returns & unfortunately, we cannot get to the underside of the steps or I'd screw up through the existing treads. (Drywall on the other side)

Either way, it looks like I'm getting a new nail gun...
Thanks,
-Mike