A Gilbert key is used to wind Gilbert clocks, made by the William L. Gilbert Clock Company, which was in business between the years 1871 and 1964. Winding these clocks is fairly basic but there are a few variations you should know about before you insert the key.
Look for the key holes. They are generally on the face of the clock. There could be one or two, depending on the style of the clock. There might be a third hole as well that adjusts the speed of the clock.
Insert the key in the winding hole and turn. It is possible that the winding mechanism could be set in either a clockwise or counterclockwise direction. Test this by winding slightly in a clockwise direction first. If you don't hear any clicks, then try the other direction.
Turn the key to wind the clock. As it starts to give resistance, slow your turns but keep going until you can't turn it any more. If there are two holes, wind them both all the way. One is for the time mechanism and the other for the striking mechanism.
Insert the other end of the key into the third small hole if there is one. This will slow or speed up the clock. Watch the clock for a few days before doing this to see if the speed needs to be adjusted. Turn the key only a small increment to the left or right to adjust it and then watch again to see if it fixed the issue. There might be a mark near the hole, such as an S for slow and F for fast, so that you know which way to turn the key. If not, you will have to guess and see what happens.