People that work with clocks have their own language. When found in a clock, we call the larger gears wheels. We call the smaller gears that mesh with wheels pinions. There is more than one type of pinion, but a form commonly found in American-made clocks is the lantern pinion.
The lantern pinion gets its name from its resemblance to an old-fashioned lantern, if viewed while holding it upright. The lantern pinion was easy to make compared to one cut from a solid piece of brass. This is why they were widely used by so many Connecticut clock manufacturers such as Seth Thomas, Ansonia, Gilbert, Ingraham, Jerome, New Haven, Welch, Waterbury, and Sessions.
The lantern pinion is made up of two disc end caps, usually brass, connected by a series of small steel bars. The end caps are called shrouds and the bars are called trundles. Over time, the trundles can become worn by the teeth of the mating wheel rubbing against them, usually with a mix of oil and dirt between them. With enough wear, the teeth on the mating gear can get jammed against the worn spots on the trundles. This can effect the reliability of a clock and even cause it to stop. At this point, I usually rebuild the pinion by installing new trundles.
The repair procedure involves removing each trundle, usually not all at once to maintain the distance between the shrouds, cutting new trundles from hardened steel on the watchmaker's lathe, installing the new trundles, and staking them in place. A worn lantern pinion can be the cause of very mysterious intermittent clock problems and NOISE. Based on the thousands of movements I have seen, many repairers leave them alone, assuming the trundles will work for another few years. This assumption is probably true, until it's not and the badly damaged movement arrives at my shop for an expensive rebuild instead of a modest priced repair. It's better to side on caution then take the easy way out.