The Clapper is the ball and shaft that swings inside a bell to strike it and make it sound. Clappers are usually made from wrought iron (WI) or Spheroidal Graphite (SG) steel, although recently there have been some successful experiments where the shaft is made partly or wholly from wood or plastic.
A clapper may have a set of raised numbers and letters on the shaft ("120K", for example). This is a manufacturing code and gives the size and material of the clapper. The number refers to the ball diameter in millimetres. The letters refer to the pattern -- 120K is the shorter version of a standard pattern 120L SG clapper. A 120J has a shorter, fatter (known as Jump or jumped) flight. Standard clapper castings range from 50mm ball to 140CB (140mm ball, counterbalanced).
You will probably also find that the clapper has a maker's name on it somewhere. Taylors, Eayre & Smith and Whitechapel foundries make almost identical castings whereas Whites' clappers are easily identifiable by their octagonal flights.
When the design of SG clappers was realised in the late 1960's. the clappers were designed and made with oversized shafts. As part of the production process this was meant to be turned down in a lathe to a nominal diameter, and thus the raised lettering/markings/maker's name wouldn't be found anywhere on the shaft. Also as a result of the turning process, the squared off block (which is up to 250mm long) on the bushed end of the clapper casting would not be apparent either, as again this is turned down to continue the round shaft up to the clapper bush with a smooth radius on both ends of the shaft. However, there is only one bell-hanging company who, as standard practice, turns every clapper down, as it saves money
The turning-down of the clapper has several effects:
- the clapper has a lower centre of percussion, and thus the bell is generally easier to get up right and handles easier (thus getting closer to the clapper dynamics of a WI clapper).
- it reduces stress points along the shaft, trying to prevent any causes of a potential fracture.
- as the clapper is reduced in weight, this improves the resonant properties of the bell, by the way in which it is struck.
This detail was published in an article written within the last year by David Marshall of Taylors, Eayre & Smith Ltd. It also highlights some misconceptions among ringers about clappering of large bells with SG clappers -- the main one being "big ball equals loud noise", which is not proportionally true. Instead, smaller clappers produce a better sound, whilst making the bell easier to ring!