Grossmann shows, in his work on the lever escapement, two sizes: (1)
Half the diameter of the acting roller; (2) two-thirds of the size of
the acting roller. The chief fault urged against a smaller safety roller
is, that it necessitates longer horns to the fork to carry out the
safety action. Longer horns mean more metal in the lever, and it is the
conceded policy of all recent makers to have the fork and pallets as
light as possible. Another fault pertaining to long horns is, when the
horn does have to act as safety action, a greater friction ensues.
In all soundly-constructed lever escapements the safety action is only
called into use in exceptional cases, and if the watch was lying still
would theoretically never be required. Where fork and pallets are poised
on their arbor, pocket motion (except torsional) should but very little
affect the fork and pallet action of a watch, and torsional motion is
something seldom brought to act on a watch to an extent to make it
worthy of much consideration.
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