Any tips on how I would know if this is a property listed screw?
If did the image does not show, it appears to be a standard screw with a washer between a double breaker.
Cut and paste from electrical panel and testing section online training course.
Also notice that the 240-volt circuit breaker is being back-fed and held in place with a properly listed holding device; in this case, it’s a screw provided by the manufacturer.
Many of our homes now require high-voltage and amperage circuits to run appliances such as dryers, air conditioning, stoves, and some load-side distribution panels, etc.
240-volt appliances are fed from two 120-volt conductors, each connected to a separate bus bar in the distribution panel. It is imperative that, when one of the circuits trips due to an over-current condition, both conductors are de-energized at the same time. If not, someone could be trying to repair an appliance that is still partially live.
For this reason, all breakers supplying 240 volts are required to have the handles tied together by a listed handle tie. Nails, screws, or scraps of wire, for example, are unacceptable. Sometimes, the breaker is molded with this connection in place, and sometimes they are linked by a listed handle tie. The inspector should ensure that the tie is present and has not been damaged.
A 240-volt circuit breaker also acts as the main disconnecting means in modern panels, disconnecting all the electrical power in the home.
The picture above is of an older Bryant panel. Also notice that the 240-volt circuit breaker is being back-fed and held in place with a properly listed holding device; in this case, it’s a screw provided by the manufacturer.