This is a 35mm concave momentary push button similar to the ones you find on arcade games.
Simple screw in design. Perfect for mashing.
The buttons has a great tactile, 'clicky' feel.

 

Features:

• Concave plunger design
• Durable nylon material
• Microswitch: max 3A @ 120 VAC
• Microswitch reliability tested to 10,000,000 cycles
• Includes 3 terminal microswitch
• Net weight: 25g

Dimensions:

• Cap diameter: 35mm
• Overall height: 65mm
• Mounting hole: 1 1/8th inch paddle bit (1.125" / 28mm)