Apple Desktop Bus Mouse
The Apple Desktop Bus™ Mouse (part number G5431) was Apple's first mouse to use their new Apple Desktop Bus. The Apple Desktop Bus Mouse was introduced with the Apple IIGS first and then the Macintosh II, the first Macintosh to feature ADB. It was an opto-mechanical mouse manufactured for Apple by Logitech.
The Apple Desktop Bus Mouse continued Apple's tradition of having only a single mouse button.
The Omron microswitch under the single button