There are two main types of movement found in tavern clocks. Here is an A-plated movement and over on the right is a rectangular plated movement. That said there are many design variants between the plates. 

In this example the there are four knopped pillars but there can be five or even very rarely six. Here we have a 4 wheel train with a standard barrel so the run time is restricted. The lower pillars are not drilled and threaded hence the hook to secure to the seatboard. The motionwork is long on the central arbor so it easily fits through the dial boards.

More often than not movements have 5 wheel trains and wind counter-clockwise. Where the train is 4 wheeled the barrel is often of a small diameter to compensate.

This example has rectangular plates and four arbors. Note the lower ones are drilled thereby allowing a securing bolt to pass through the seatboard. The central arbor is short which in this case resulted in the dial boards being gouged out to allow the motionwork to pass through. The hour wheel is part weighted for no obvious reason. The front plate has three spurious holes which indicate another use in the past. This has a 4 wheel train with a smaller than average barrel so the clock runs for 8 days; heavy weight.

Careful inspection of the movement and how it is fitted to the case is an important aspect of assessing whether the clock is a marriage. That is a whole subject in its own right.