What Type & Size of Key Do I Need ?

A Rough Guide to the type and size of clock key for your Clock

Clock keys are sized using two different methods.

1 Number sizes

The number sizing system seems to have evolved many years ago with the number on the key corresponding to a size on a chart. This system comes unstuck when you find out there’s at least three different scales, all slightly different, starting from different points, meaning a No 8 key made by one manufacturer will not be the same as a No 8 by another.

2 Metric Sizing

The Metric sizing system is a much more straight forward way of selecting the size of key you require. The size stamped on the key refers to the size of the internal square in the key (across the flats) meaning if you have a clock with a 4.00mm winding arbor, you just buy a key to fit. The keys in the metric system rise in 0.25mm (one quarter millimetre) increments, 3.25mm, 3.50mm, 3.75mm, 4.00mm and so on.

Which size does my Clock need ?

The simple answer is, we don’t know, but the following may enable you have an educated guess.

The best way is to measure the winding arbor (the steel shaft the key fits on to) . If you have a set of venire callipers, and you can get them on the end of the winding arbor, you can get an accurate reading and select a key. It is worth remembering that most winding arbors taper out towards the clock, and the end section is most likely the smallest. This is advantageous because it makes the selection of the size less critical, up to a point anyway, as the key will slide onto the shaft until it reaches the ideal point..

More modern clocks (1900 and later) have less of a taper. On clocks earlier than this, especially Long Case or Grandfather Clocks, the taper on the winding arbors can be quite steep meaning guessing the size of the key is quite a challenge.

How do I select the correct size when I can not see, or measure the winding arbour ?

The only way in this case is to size it using the original key, or another key you might have access to. This means that you will at least know whether you need to go larger or smaller, and roughly how much.

At Wardles, we will exchange any key we have supplied to you, only asking that the clock key is returned in its original condition, and you put enough stamps into the package to post the clock key back to you.

Which type of key would suit my clock ?

The style and design of a particular key means it will not always be suitable for every clock.

Mantel clocks & French clocks will use either a standard Brass butterfly key or Steel bow type key. A few Mantel clocks have quite powerful springs in them, putting lots of strain on the key and fingers of the person winding them, we would recommend a Steel bow key is used for the more powerful springs, as they are considerably stronger than the Brass. Our steel keys are manufactured with extra thick, strong handles to resist twist & bending, which affects other cheaper imported keys.

Long Case Crank keys, with Steel or wooden handles, as suggested by their name are used to wind long case (Grandfather) clocks. They are designed with a long crank to make it easier to wind up the heavy weights used to drive the Long Case clocks, time, & strike trains. The Steel handled key we manufacture is based on a quite early design, and the wooden handled key is based on a design from around 1800 onwards.

One of the factors, apart from sizing that should be taken into account when purchasing a Long Case clock key, is the length of the pipe which locates on the winding arbor. This should be long enough to rise the crank and handle assembly above the clocks hands, otherwise this will make the winding of the clock a laborious process, with the person winding only being able to wind the clock a few degrees before repositioning the key, or worse damaging the clock hands and face when the crank strikes them. Both of our designs have longer pipes to prevent this on the vast majority of Long Case clocks.