For my layout, I use a #4 wood screw in whatever length holds the track down properly.  I start out with 3/4 inch length and if it loosens up, go to 1 inch, 1 1/4 inch, or all the way up to 1 1/2 inch.  The last two sizes go through the ceiling tile base that I use into the plywood below, so the track isn't going anywhere.

what type of waffleboard do you have?

I see that the name describes several types designed for specific uses.

What is waffleboard? I have never heard the term. Celotex?

I think the OP might have meant --  waferboard -- , another name for OSB.

BatTrain posted:

I think the OP might have meant --  waferboard -- , another name for OSB.

How would you know?

geysergazer posted:

What is waffleboard? I have never heard the term. Celotex?

I'm using 9/16

Oriented Strand Board  for a surface

Ron's suggestion for the #4  flat head Philips sheet metal screw is spot on - You may want the loner length 1" - 1 1/4" to be certain that they bite in the OSB.

be careful of splinters handling or working with the OSB - 

here is a supplier that I use for the screws - black oxide flat head

Different screws available.   #6 screws, top, including drywall screw, #2 at the, bottom, #4 middle.   Long round head screw second from bottom is an Atlas track screw.