Hinged wooden clamp
Bicycle inner tube
There are several different methods of silencing a bell in common use. Hinged wooden clamps, secured to the bell with a wing nut locking mechanism, can clamp the clapper in the centre of the bell and are easy to make. These can sometimes work loose if not tightened properly and need to be tailored to fit the diameter of each bell. One disadvantage of clamping the clapper centrally is that it makes the bell lighter set on both strokes, as the weight of the clapper is not working so effectively at holding the bell on the stay.
An alternative method is to cut an old motor-cycle tyre into sections. Old tyres are easy to get hold of as garages need to dispose of them and they produce a heavily muffled sound on both strokes. Not being fixed centrally means that they do not affect the set of the bell.
Bicycle inner tubes act as a large rubber band and can be used to hold the clapper centrally or to one side. They are relatively cheap and quick to fit and remove, the top end being looped over one of the nuts on the headstock. If the tube is too long, you can shorten it by tying a simple knot in the middle of the tube.