Clock Key Size Gauge

Mechanical Clock Keys

Mechanical clock keys are the clock parts that are most frequently lost. Once the clock key is no longer with the clock, it always seems to disappear. With the below information you can order a new key utilizing the clock key size chart.

Getting the Right One

We have mechanical clock keys in all the sizes available. Between the key chart or the movement type information below, you have a good chance of finding the perfect key. The movement type includes if the clock is made in Germany or USA and when it was made.

This is the fastest and most easiest way to get the clock key. The further back in time we go with clocks, the more we would need to rely on the key chart instead. There will be a stamp with the country of origin on the back plate of the movement and this can help us get the key.

How to find the Right Key for Hermle Movements

Clock Key Required by Hermle Movement Number

Use this Clock Key Chart to quickly identify the correct key number and type based on your Hermle movement ID number. Ensure a perfect fit for winding your clock!

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Keys for German Units Post WW2

German made post WW2 movements that are square or rectangle will take a number 8 key or crank.

If the clock movement is round and made in Germany the key size is number 4. Some round ones will take a number 3 but if getting a 4 it will still fit and wind the clock either way.

Keys for USA Units 1900 – 1950

American clocks made from around 1875 until after the second war almost always take the size 7 clock key. The number 7 keys fits the 8 day time / strike units pretty much every time and this is what USA made the most of. This rule may not apply to Westminster (3 places to wind) or time only (one place to wind) clock movements.

Keys for Korean and Chinese Clocks

Size 7 for these units usually. All the 31 day clocks with Asian movements and also US replicas made in India, all take size 7.

The Over Wound Myth

Of course, if a clock is not working, people wind it up all the way in attempts to make it run. Everyone winds it up, but the clock still doesn’t work, so it remains wound up.

The only way a clock can be overwound is if someone winds it up for so long that the mainspring becomes stuck.

Double-End Clock-Key F-S Note

The following is a Double-End Clock-Key F-S Note that will be very handy. Some clocks have a small place that looks like a mini clock winding arbor at the 12. It may say F/S or A/R. The F/S represents fast or slow, and the A/R represents advance or retard.

This controls the timing of the clock and turning it to fast or advance makes time faster and the opposite for slow. An ideal double end key fits both the winding arbor to wind the clock and also fits the smaller time regulator aspect.

This is not easy to get and at the same time is the most lost part. It is possible to regulate the clock another way with an adjustable bob instead of a fixed length bob.

Get the double end key the hard way

Using the clock key size chart, get the right size that the clock requires. This chart works for both the fast/slow regulator and also to wind the clock.

However, this is not easy because it requires a measurement of the post the double end key fits onto. In order to get this measurement remove the clock movement or the dial. Without access to the front of the movement it is hard to measure exactly how wide the arbors are that the key is to go on.

Double end clock key the easy way

There are many sizes and combinations for the double end key and it may be tricky to get the right size. Sometimes it is best to just get the 4 pack of double end keys we offer

. These are the top 4 most common double end clock keys so the odds are one will be the correct key. Ideally this will supply the clock with a key that fits both the F/S regulator and the winders. However be aware this 4 pack does not guarantee one will work.

Double-End Clock Key F-S Note Continued – An alternate method

It is possible to forget the whole double end key game and use a single end key instead. It does make things easier and is a better long term solution.

Inevitably, once the perfect fit the key will get lost again. This seems to be the trend of what happens. Once the key is separate from the clock, there is a higher chance of it getting lost. Many times we suggest putting the key in the bottom of the clock case for safe keeping

Using an adjustable bob instead

The solution to the double end key problems is to get the single end key to wind the clock. Also get the adjustable bob. The adjustable bob can be regulate the clock with the pendulum instead.

The bob will have a nut on the bottom. Raise the bob on the pendulum to speed up time. The opposite is true for slowing time down. Once regulating the clock, it will stay this way for the most part. Some timing may or may not need to be done when the temperature changes vastly.

For the most part, time the clock and it will stay that way within a couple of minutes a day all year long. The adjustable pendulum bob comes in three sizes, or bob diameters. The middle or smaller diameter bob is fine for most clocks because the weight is not as important as the length.

Parts available to purchase

Other parts to consider besides the double end clock keys. We have two styles of the adjustable pendulum bobs. One of them is the three sizes of bobs that have the nut underneath. We call this the Adjustable Mantle Clock Bob.

There is another style bob that is adjustable from the back side. We just call it the Adjustable Antique Style Mantle Clock Bob. They both function the same, it has a bob on the pendulum that can regulate the time.

The part they hang onto is usually a long wire with flex spring steel on the top. This gets bent and cut into shape for the proper length. It comes in a three pack and we call them the Long Suspension Spring Rods.

Clock Key Size Chart Explanation

Clock keys have there own number system from 000 to 16 as seen in the Clock key size chart. However the number does not indicate what size is what number and can be confusing. So how do you use the Clock key size chart to get the right key?

It would make more sense if the key size was the MM of how wide the key was to fit, but this is not how it works. This section is to figure out what key number to order so the clock can be wound up. Subsequently, the clock key gets lost the most out of any other clock part.

Of course, it can be tricky to find the right key for your clock because there are many sizes. The Clock key size chart will give us the right size key to order.

Double End Clock Keys

In addition, some keys have two sizes on one key and this is called a double end key. By and large, the clock key size chart will work for both the wind up part of the clock and also the smaller F / S portion. When the clock has a F / S regulator portion it will be at the 12 o’clock on the dial.

Alternately, if there is a small arbor inside of a hole at 12, this is the time regulator control and the key would have two ends. Thus, it may say F / S at this location or A / R. F / S stands for Fast or Slow, or it could say A / R to stand for Advance or Retard and is referring to the timing of the clock.

Of course, if the clock is running fast in time, turn more to the Slow or Retard direction to slow it down. Refer to the Clock key size chart with your measurements to find a key to work with this function.

Getting the Right Clock Key Size

Given these points, to get the key needed, measure the shaft the key is to go on to, then use the Clock key size chart to get the key size needed.

Please do not call asking what key the clock needs, as you will be told it would still have to be measured. In short, measure the shaft that the key goes onto in MM and then use the clock key size chart to match it up.

The Lazy Way Instead of the Clock Key Size Chart

The Clock key size chart has all of the sizes listed however sometimes certain key sizes are known. Generally speaking, almost all post 1960 mechanical clocks, made in Germany take a size #8 key or crank, unless the movement is round.

Ordinarily the round ones take a number 4. The American time strike antique units mostly take the size 7 key. Match your measurements to the Clock key size chart to be sure.