Not historian, but I have a general interest in (and too many!) clocks.

I suspect you will not find a definitive answer. Features such as the flat spring and catch detent clicks on clocks will have varied between makers over a long period of time. Changes will have started in the higher end clocks, and only very gradually percolated to cheaper or more provincial makers.

I would guess that the first makers to use the flat spring would be those that made 8 day and/or fusee clocks – both of which typically use that style of click. They would have had the parts available/designed and consequently used them on any higher end 30 hour clocks. I would expect the first ones to be made in the early 1700's.

30 hour clocks with circular springs were still being made into the 1800's. I recently cleaned my French lantern 30 hour clock which dates to 1820, and that uses circular clicks. They would probably have stopped being made only when factory made mass production clocks became commonly available in the middle of the 19th century.

So say between 1710 and 1850 would be the changeover period.

You could try asking on the NAWCC forum (you don't need to be a member to sig up), or one of the clock forums on the internet.

Edited By Peter Cook 6 on 30/03/2021 14:17:42