Clock Key Sizes

Clock key sizes come in 2 different standards, just to make it confusing.

When buying a clock key you will need to know the right size for your clock.

It is essential to get the right size of key, too small and it will not fit on the winding  arbour but to large and the key can slip and round out  the square your clock or worse still slip and damage the clock and your hand!

If you have the old key and it no longer fits or is damaged, it may have a number on it. If it is a single number it is the old imperial size, if it has a decimal point it is the size in mm.
In this case just re-order the corresponding size.

If the key does not have a number on it you will have to measure the internal square. To find the correct size of winding key you need to measure as accurately as possible the side of the square where the key fits then add 0.5mm.   Some people find it easier to push some blue tack on to the square and measure the imprint to the nearest quarter of a mm.