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.