The lever that Tom Sendall refers to is a speed control.  The wire
rivetted to the bottom of the lever should be in the form of a spring,
including a small loop, the end of which holds the felt pad.  This felt
pad should not touch either the stop wire or the fly.  It is designed
to rest against the shaft of the fly and impart a small degree of
friction and thus resistance against rotation.

Movement of the lever will impart a variable force onto the felt pad,
via the deflection of the wire spring, and hence act as a speed control.
The lever's pivot should be stiff enough to hold the lever in any
desired position.  It is simple, but effective.

Nicholas Simons, GB