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 it was 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. That's what the lantern pinion shown above needs. This one is connected to the fan in a cuckoo clock, which helps to regulate how quickly the bird figure performs its action. This is being done as part of a comprehensive overhaul of the clock am am doing for a customer.
The repair procedure involves removing each trundle (often 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 locking them in place. A worn lantern pinion can be the cause of very mysterious intermittent clock problems. Based on what I've seen, many repairers leave them alone, assuming the trundles will work for another few years. This assumption is probably true, until...one day, it's not.