clock & barometer repairs
01277 658800 Billericay
clock keys
Key types
Apart from the images that one usually conjures up of a clock key, some short like the first two opposite and some long like the next two, there are three very different styles.
Double-ended keys are mostly designed for French clocks. On French carriage clocks the smaller end is used to turn the hands for resetting the time. On bigger French clocks, the smaller end should fit the tiny steel square that protrudes above the 12. This is the Brocot regulator for fine-tuning the timekeeping; it can be turned clockwise to make the clock run faster, or counter-clockwise to make it run slower.
Then there are heart-shape keys which are traditionally found on dial and bracket clocks fitted with a fusée movement.
Crank keys (bottom pair) give more leverage but place additional stress on the winding square so should be used with caution (not like a fishing reel) and only on longcase clocks and Vienna regulators as a rule. You sometimes see them used on large bracket clocks but it is not advisable.
Key sizes
Clock keys can often be difficult for the owner to replace because as well as the different key types, there is no such thing as a 'standard' size clock key. If you need a replacement, I can help but you'll need to measure the size of the steel winding square that you see in the winding hole. Often these are recessed in the dial so they can be difficult to reach to get an accurate measurement. And on older clocks the shaft is often tapered so allow for this where you cannot remove the dial. You'll need an accurate measurement because clock key sizes increase in increments of a quarter of a millimetre!
Use a micrometer or a Vernier gauge if you have one and then send me the details; if you're prepared to take a risk, make an impression of the size using blue tack and measure that instead. But remember, if your key is too small it simply won't fit on the square so be cautious of under-estimating; on the other hand, if it's too big it will damage the square over time by rounding off the corners and might even slip round.
In England, keys are sized in the following way:
mm square |
key size |
|---|---|
2.00 |
00 |
2.25 |
0 |
2.50 |
1 |
2.75 |
2 |
3.00 |
3 |
3.25 |
4 |
3.50 |
5 |
3.75 |
6 |
4.00 |
7 |
4.25 |
8 |
4.50 |
9 |
4.75 |
10 |
5.00 |
11 |
5.25 |
12 |
5.50 |
13 |
5.75 |
14 |
6.00 |
15 |
6.25 |
16 |
6.50 |
17 |
6.75 |
18 |
7.00 |
19 |
7.25 |
20 |
However, in the US, they use a different numbering system and makers do not always stamp their keys accurately so it's always best to go by the actual measured size. If you're struggling to measure the square and can't bring the clock to me, I suggest you take the clock to your nearest clock dealer and he'll try out different sizes for the best fit and tell you the size for no charge. Dealers all accumulate a range of different keys over the years so he may offer to sell you one that he already has or to get a new replacement one for you. Expect to pay somewhere between £5 and £25 depending on age, condition, and type.
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