Malmark also tries to keep the mechanism short enough that the clapper assembly is entirely inside the bell so that the bell can be stood on end. Where in the chromatic scale to change from one clapper head to another is hard to determine and, indeed, may vary from set to set. The old rubber heads harden and crack with time, which leads to a deadened tone. Felt squashes, of course, so it needs to be replaced occasionally. Most of the materials used for clappers these days probably wouldn't be hurt by temperature extremes, but the action probably will be sluggish if very cold.
Some metal is left attached to the top of the bell in the casting process.
This gives the factory something to grab ahold of while tuning and polishing the bell. There is some controversy among the manufacturers about what to do with the tang. TR feels that it has no effect on the tone quality of the bell, so its presence or absence is purely a matter of convenience, weight, and aesthetics. The major differences between bells produced by the various makers are in the casting profile and the clapper mechanism. Malmark chooses to try to push undesired overtones to frequencies as high as possible.