DATA COMMElectronics 45-0006-WH Hole Saw Plate - White

Will the wings work in a solid wall passthrough of 1 3/4 in. diameter (not drywall)?

How many plates come in a pack?

This item is out of stock and still allowed me to purchase it. why?

Can you use this on a 3/4" piece of plywood? Will the locking tabs in the back work properly with a 3/4" plywood?