I'm looking for a large spring-loaded button, styled like the emergency-stop buttons you might see on a wall for a gas station or workshop - like the one shown below. However, I have no idea if I could use one like that with the arduino, as far as electrical components. I just need it to make contact to activate as a MOMENTARY switch. When the user hits it, it starts off my process. I need something big, like 2-4 inches in diameter like in the link, not the tiny little momentary buttons that are 0.5 inches.
I found a few on digikey.com but they are plastic buttons, not metal. That might just be a limitation I'm going to hit.
Search “mushroom head pushbutton”. Be prepared for non-hobbyist pricing.
22mm is the most common standard size, so be prepared for the price to go up quickly when it gets larger.
Here's a cheap one.
It might be easier to purchase a small pushbutton and make a custom head.
All emergency stop button switches lock in the open position and must be manually turned to be relaesed back to the normal operation. Probably don't want that.