I believe a common gear used is a cycloidal gear for various reasons.
check: http://www.gearshub.com/cycloid-gears.html
Molecular Clock
Use Wingardium Leviosa.
You go inside the clock tower, make your way to the top, use the oil can, and grease the gears that directly connect the two large gears.
You go to the clock tower that guys working on and go inside. Then you will use it to oil some gears at the top.
Smash it on the ground until it is in pieces, then there should be some gears out.
You only have to oil the middle gears until you can't oil those gears anymore.
clock.
the gears in the clock tower
A clock ticks when its mechanism releases stored energy at regular intervals to move the gears and hands. This rhythmic movement of the gears is what creates the familiar ticking sound in most mechanical clocks.
Clock gears are typically made of steel, brass, or plastic, depending on the specific design and purpose of the clock. Steel gears are more durable and long-lasting, while brass gears are often used in higher-end and antique clocks for aesthetic reasons. Plastic gears are commonly found in cheaper and modern clocks.
Inside the clock tower at Diamond Plains, the clock gears are rusted. You oil only the center set of gears, not the ones that go around the outside. Click on each only until it sparkles, and do not waste oil by missing the gears. When you are done, turn the handle to start the gears and get the clock working again.
You have to get the oil can at the Trade and Barter shop, go to the clock, and make all the gears between the two big gears shine.