Brass Single-End Clock Key

Mechanical clock keys

Mechanical clock keys is the clock part that is most frequently lost. Once the clock key is separated from the clock it always seems to end up missing. With the below information and the clock key size chart a key can be ordered.

Getting the right one

We have mechanical clock keys in all the sizes available. Between the key chart or by movement type information below, the chances are good of getting 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 the key chart would need to be used instead. The country of origin would be marked on the back plate of the movement and this can help us get the key.

Keys for German units post WW2

Germany post WW2 movements that are square or rectangle will take a number 8 key or crank. If the clock movement is made in Germany and it's round the key size is number 4. Some round ones are supposed to take a number 3 but if you get 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 any clock that is not working will be wound all the way up from trying to make it run. Everyone winds it up and the clock does not work so the non working clock is always wound up. The only way a clock can be over wound is if its been wound up for so long that the mainspring stuck. When the mainspring is stuck together to itself with rust and goo for so long it may stick that way. This is rarely the situation and usually the clock would have rust on it if the mainspring is so wound up it will not wind down.

Double End Clock Key (F / S at 12) Note

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 this means fast or slow, and the A / R would represent advance or retard. This controls the timing of the clock and turning it to fast or advance makes time faster 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 you can get the right sizes 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 key fits onto. In order to get this measurement the clock movement or the dial needs to be removed. Without front of the movement access it is hard to measure exactly how wide the arbors are that the key is to go onto.

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. So you may just want to get the 4 pack of double end key we offer. This is the top 4 most common double end clock keys that are used so the odds are with you that you will get 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 success but is more of a by chance game.

An alternate method

It is possible to forget the whole double end clock key game and use a single end key instead. It does make things easier and also better for a long term solution to this issue. The reason it is best for long term is because after getting the perfect key it will be lost again as this is what happens. Once it is separated from the clock in anyway, it stands more of a chance of being lost.

Using an adjustable bob instead

How this way is handled is to get the single end key to wind the clock, and also an adjustable bob. With the adjustable bob you can regulate the timing of the clock with the pendulum instead. The bob will have a nut on it and to raise the bob on the pendulum will speed up time. The opposite is true for slowing time down. Once the clock is regulated, it will stay this way for the most part. Some timing may or may not be needed when the temperature changes vastly. For the most part the clock can be timed and it will stay timed within a couple 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

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 desired 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. However the number does not indicate what size is what number and can be confusing. 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. The clock key gets lost the most out of any other clock part. It can be tricky to find the right key for your clock because there are many sizes. The chart will give us the right size key to order.

Double end clock keys

Some keys require two sizes on one key and this is called a double end key. The below clock key size chart will work for both the wind up part of the clock and also the smaller F / S portion. You can tell if your clock has a F / S regulator portion by just looking at the 12 o'clock on your dial. 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. 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. So if the clock is running fast in time, you would need to turn more to the Slow or Retard direction to slow it down.

Getting the right key

To get the key you need, measure the shaft the key is to go on to, then use this chart to get the key size # you need. Please do not call asking what key your clock needs, as you will be told it would still have to be measured. Again, you are measuring the shaft that the key goes onto in MM and then using the below clock key size chart.

The lazy way

Almost all post 1960 mechanical clocks, made in Germany take a size #8 key or crank, unless the movement is round. The round ones take a number 4 usually. The American time strike antique units mostly take the size 7 key.

• 1.75mm = 000 Key
• 2.0mm = 00 Key
• 2.25mm = 0 Key
• 2.5mm = 1 Key
• 2.75mm = 2 Key

• 3.0mm = 3 Key
• 3.25mm = 4 Key
• 3.5mm = 5 Key
• 3.75mm = 6 Key

• 4.0mm = 7 Key
• 4.25mm = 8 Key
• 4.5mm = 9 Key
• 4.75mm = 10 Key
• 5.00mm = 11 Key

• 5.25mm = 12 Key
• 5.5mm = 13 Key
• 5.75mm = 14 Key
• 6.0mm = 15 Key