The top hook is the very top of the pendulum that will enable the pendulum to hang on the leader. To clarify, the leader is the 4 to 7 inch long bar that drives the clock pendulum back and forth.
What they fit
In fact, most of the top hooks here fit German post WW2 mechanical pendulum clocks. There are some top hooks that are for, or can only be useful on antique clocks.
It matters only that the pendulum can hang into the air onto the leader and be stable. Antique clock pendulums can use any one of these top hooks if it will do the job.
How to install
The top hook installation is by friction only. Bend the tabs over and use a punch and a hammer to secure it to the wood stick. Another way is to drill starter holes into the top hook and secure with screws or nails.