Clock Keys

Finding the right clock keyDouble End Clock Key (F / S at 12) NoteHow to use the clock key chartThe clock key chart

Mechanical clock keys, get the right one

Here we have mechanical clock keys in all the sizes available. We get many calls asking what key their clock takes and over the phone it is difficult to say what key size is needed.

Best to read the below text on how to use the clock keys chart and get the correct sized key to wind your clock. What can be said is most larger German movements take a number 8 key.

So if your clock movement is made in Germany, is 5 x 5 square or 6 x 9, it will take a number 8 usually. If the clock movement is made in Germany and it's round, it's usually number 4.

If you have a 31 day clock, or a Korean clock, or a commonly produced early American time strike movement, then it's usually the number 7 mechanical clock keys. However, if you want to be sure with all this then use the below chart.

Another thing to note is you cant over wind a clock. It is just not true that a clock can be over wound, this is a myth. If the clock is wound all the way up and it will not function, it is not because the clock is wound too much. Of course any clock that is not working will be wound all the way up as anyone who tries to get the clock to work will first wind the clock to get it going. 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 together to itself with rust and goo for so long it sticks 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. But otherwise, there is some other issue with the clock such as being out of beat or in need of a clock cleaning or bushings.

- - The content of this web page and web site was written and copyright by James Stoudenmire of - It may not be used commercially without permission. - -

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

If you see an F / S or an A / R around the 12 o’clock area of the clock dial, this is called a regulator. So for F / S this means fast or slow, and the A / R would represent advance or retard.

So turning the arbor toward F will make the clocks time run faster and the opposite direction for slow. To turn this you would use the small end of your clock key. If the key has been lost at one point then someone could have replaced the key with a single end key instead of double. The double end key is what you would need instead, one for the winding up the clock and the other side for the F / S regulation. 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 with both sides fitting your clock movement.

If the pendulum leader is too short then you may need to adjust the fast / slow beyond what the regulator is designed to adjust. If this is the situation you may just want to get an adjustable bob to regulate the clock instead. If you get the adjustable bob instead you do not need a double end key. You only need to adjust the nut on the bottom of the pendulum bob as to raise the bob to speed up the clock time or the opposite to slow the clocks time down. So if you choose to get the adjustable bob, please see it displayed at the following link. The adjustable pendulum bob comes in three sizes, or bob diameters. Usually the middle sized bob or the smaller bob is fine for most clocks.

- - The content of this web page and web site was written and copyright by James Stoudenmire of - It may not be used commercially without permission. - -

Clock key size chart to get the right key

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 and also some have two ends on them. The type of clock key that has two ends on it is called a double end key and this is the most difficult to find the right fit. The below chart tells us what size key to get for either the wind up portion of the clock and also works the same for the F / S regulator side of a double end key. You can tell if your clock has a F / S regulator portion by just looking at the 12 oclock on your dial, if there is a tiny arbor there to turn, this is the F / S. The F / S stands for Fast or Slow, or it could say A / R to stand for Advance or Retard. This of course 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 some.

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 chart.

Shaft width / Key #
  • 1.75mm = 000 Key
  • 2.0mm = 00 Key
  • 2.25mm = 0 Key
  • 2.5mm = 1 Key
  • 2.75mm = 2 Key
Shaft width / Key #
  • 3.0mm = 3 Key
  • 3.25mm = 4 Key
  • 3.5mm = 5 Key
  • 3.75mm = 6 Key
Shaft width / Key #
  • 4.0mm = 7 Key
  • 4.25mm = 8 Key
  • 4.5mm = 9 Key
  • 4.75mm = 10 Key
  • 5.00mm = 11 Key
Shaft width / Key #
  • 5.25mm = 12 Key
  • 5.5mm = 13 Key
  • 5.75mm = 14 Key
  • 6.0mm = 15 Key

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.

- - The content of this web page and web site was written and copyright by James Stoudenmire of - It may not be used commercially without permission. - -