The instructions say 1 inch, but I think that's too small. My installer went slightly larger, and it fits fine. I wouldn't recommend drilling larger than 1-1/2 inch.
Hi CBRJM, Thank you for your recent inquiry with The Home Depot. All our products that we sell online and at the store , should be same priced unless it's been markdown or on clearance. This model #EV-AirSwitch-Ni shows that it is an online item only. Not sold in stores. Hope that helps. We appreciate your business and look forward to serving you in the future.
This switch is rated for up to 15 Amps and should be sufficient for all standard consumer disposers models.
The second outlet is for an accessory like an instant hot, and is normally on. They are switched opposite, so when the disposal is on, the accessory is off.
The threads will allow for about 2-1/2 inch countertop thickness. Total clearance (including counter thickness) is about 4 inches.