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. 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.

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


The content of this website is copyright by Clockworks and written by James Stoudenmire in year 2020

Updated on: 05/08/2022