Wiper arms, unlike wiper blades, are the actual arms at the base of the blades that move them across your windshield, pushing rainwater and other obscurities out of the way. Wiper arms are typically much sturdier than blades, but over time, they can rust and be detrimental to the aesthetic appeal of your car. Replacing the arms on a Mazda Miata, which has been in production since the 1990s, takes only a few minutes if you have the right tools in place.
Remove the wiper blades by pushing down the tab at the base of the blade and then pulling the blade off the arm.
Pull back on the wiper arm until it locks into a vertical position.
Remove the retaining bolt at the base of the wiper arm using the socket wrench and socket and pull the arm off of the motor, which manoeuvres the arms.
Slide the new arm into the place of the old one and tighten it using the same bolt.
Put a blade back onto the arm -- preferably a fresh one -- and push it back onto the windshield. Repeat steps 2 through 5 with the other arm.
Miatas have changed over time and therefore you may experience slight differences when dealing with the wiper arms. However, the general practice remains the same and locating the retaining bolt at the base of the wiper arm is an easy task no matter what model Miata you have. Some people like to repaint their wiper arms in lieu of replacing them entirely. This may be economical, but make sure you do your research as to what's best for you before proceeding.