Further to the last entry, I wondered how an auctioneer’s hammer – the British equivalent – was taken to the USA and became a gavel, and I also wondered what the judge actually does with the gavel. Wikipedia was helpful here:

A gavel is a small ceremonial mallet commonly made of hardwood, typically fashioned with a handle and often struck against a sound block to enhance its sounding qualities. It is a symbol of the presiding officer’s authority and right to act officially in his capacity,[1] and as such, is used by presiding officers—notably chairmen and auctioneers—to call for attention or to punctuate rulings and proclamations. It is customarily struck to indicate the opening and closing of proceedings, giving rise to the phrase “gavel-to-gavel” to describe the entirety of a meeting or session.

Apparently there are rules on how to use the gavel:

Robert’s Rules of Order Newly Revised provides guidelines on the proper use of the gavel in deliberative assemblies. For instance, the chair is never to use the gavel in an attempt to drown out a disorderly member; … rather, the chair should give one vigorous tap at a time at intervals. … The chair should not lean on the gavel, juggle or toy with it, or use it to challenge or threaten or to emphasize remarks.[ …The prohibited practice of a chair cutting off members’ right to debate or introduce secondary motions by quickly putting a question to vote before any member can get the floor is referred to as “gaveling through” a measure.

Richard Nixon broke the Senate’s 1789 ivory gavel in a heated debate on nuclear energy.