Okay this one is straight forward, here are the parts of a typical mechanical keyboard from top to bottom physically.
Keycaps, switches, plate, PCB, and case.
Keycaps
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Keycaps are the first thing you see on the keyboard, they are the piece of plastic with alphabets and numbers on them that u press. Typically in black or white but comes in much more colors in the custom world. Click here to read more on keycaps.
Switches
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Switches are literally what the name implies, they switch the keys on or off, so when you press “W” it literally turns on W on the electronic circuit board to send the signal to your computer or phone. There are 3 types in general + silent variants. Read more about switches here and here.
Plate
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The plate is used to hold the switches in the right place, and in customs we use different materials for different sounds and typing feel. However, not every keyboard has a plate, as many gaming keyboards use an “integrated plate” where the plate and case are a single component to save costs and results in a keyboard that doesn’t sound very good. Read more about keyboard plates here.
PCB
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This is straightforward, it’s basically just a circuit board that turns your key press into something your computer recognizes and sometimes make really pretty lights too.
Case
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It’s a case lol. It holds everything together. The material of the case can drastically change the feel and sound of a keyboard. Read more about case material here.