Parker Fly Handbook page 26

STEP 5
IMPORTANT
Make sure the spring block is still touching the step-stop while the strings
are in tune.
(If necessary, tighten the balance wheel until the spring block is touching
the step-stop and retune. Repeat as necessary, but do not over-tighten.)
— WARNING—
Do Not Over Tighten Spring
Over tightening the spring may cause permanent
damage to your Parker Fly. If you can see 15
threads or 3/4" (19mm) the spring may be over
tightened.
Repeat steps 1 through 5 checking the following:
• Does the string gauge match the spring number? (Note: alternate
tunings may change spring performance).
• Is the step-stop in the H O M E position?
• If the spring is still over tightened, replace it with a stronger spring.
Only tighten the spring against the step-stop when
the step-stop is "down" in the H O M E position.
The step-stop "up" position is only for BALANCED
mode use.
Do not proceed, unless the strings are in tune and the step-stop is in the
H O M E or BEND DOWN position.