VideoGamesNewYork is trying here to build a decent knowledge on arcade parts and on how to modify your arcade stick or build one from scratch. It's an ongoing work and it require a lot of time so we hope to be as exhaustive as possible as well as precise.
Let's start with defining the parts we are going to use on most of our arcade projects:

Buttons (electrical switches operated by pressing a button, which closes or opens a circuit)
We have generally 2 types of buttons: Snap-in, and Screw-in.
All the buttons are composed by 3 parts:
1) The circuit board
2) The plunger (the small plastic disk that you push with your finger
3) The base (what connect the Plunger and the circuit board to a surface0
Snap-in and Screw-in differ on the 3rd component, the base.
On the Snap-in the base secure to a control panel with tabs that “grip” onto certain material thicknesses
On the Screw-in the base secure to a control panels with a threaded nut

Joysticks
A joystick is an input device commonly used to control video games. Joysticks consist of a base and a stick that can be moved in any direction. The stick can be moved slowly or quickly and in different amounts.

Microswitch: An electronic component found in both joysticks and buttons that when activated complete a circuit between the ground and signal connection.

PCB: Printed Circuit Board. Some joysticks have microswitches connected to a PCB and used pinned output instead of tabs or direct soldering to microswitches.

Mounting plate: Metal plate attached to the base of the joystick. This is mounted to the control panel with the use of screw or nuts and bolts.

Wire harness: A molex connector that is used on certain joystick PCBs. Sanwa manufactures JLF-H and Seimitsu manufactures H5-PIN. They are pretty much exactly the same.

Restrictor/gate: Device that restricts the movement of the joystick to a specific pattern or shape.
Generally Restrictor gates can be:
Square: The standard for joysticks. This has corner/notches in the up-right, up-left, down-left, and down-right directions only. Being a square, the distance from the center of the gate to the corners is longer than the distance from the center to up, down, left, and right directions.
Octagonal: This has defined corner/notches in all 8 directions. Each notched direction is equidistant from the center. Sanwa's octagon restrictor for the JLF series is the GT-Y. Circular: This has no defined notches making a perfect circle path. Every possible direction is equidistant from the center; however, this does not mean that the stick recognizes all possible directions.

HOW TO CHANGE BUTTONS ON YOUR FIGHSTICK