These are almost certainly a standard larger screw base, internationally known as E40. Also called GES in the UK or Mogul screw base in the USA.
Less used than in years gone by but still available on fleabay and elsewhere if using the above search terms.
These sound like series street lighting bulbs. Each lamp runs at a very low voltage but large numbers are burnt in series from a constant current high voltage supply.
Very little used these days.