Honda HHT35S Owner's Manual page 22

If you are not sure if the lines have snapped out of the notches,
gently pull the spool away from the housing about an 1/8 inch to
inspect the lines. If necessary, gently pull each line until your hear it
snap out of the notch.
OUTER
DRIVE
10.Hold the housing and rotate the spool in the direction of the arrow
to lock the round lug into the half-round locking hole. Trim the lines
so they are equal length.
Removal and Installation
This section shows you how to remove and install either style trimmer
head from your trimmer.
1. Insert the tip of a 4 mm hex wrench, or equivalent, fully into the
gear case hole.
2. Turn the trimmer cutting-line head until you feel the tool drop into
the hole in the cover plate/spacer A. Verify the trimmer head does
not turn.
3. All output shafts use left-hand threads. Make sure the tool remains
in the hole, then grasp the trimmer head and turn in the direction of
the arrow to remove.
4 mm HEX WRENCH
GEAR CASE
(commercially available)
22
CHANNEL (2)
ROUND LUG (2)
METAL
EYELET (2)
HALF-ROUND
LOCKING HOLE
REMOVAL
DIRECTION
TRIMMER
HEAD
4. Remove spacer B and cover plate/spacer A from the output shaft.
Note the order and orientation of each part as you remove them.
CUTTING-LINE HEAD
SPACER B
COVER PLATE/
SPACER A
5. Installation is the reverse of removal. Always clean debris, dirt,
loose line, etc. from the trimmer head and output shaft area before
installation. Tighten the trimmer head securely.
Blade
Blade Inspection
Always wear gloves when working around the blade. Before each
use, check the blade for wear and damage, and check the tightness of
the blade lock nut. Examine the entire head area, including the debris
shield, and clear or clean it free from dirt, debris, loose string, wire, or
any other foreign
materials.

WARNING
A worn, damaged or cracked blade can break, and pieces
of the damaged blade can become dangerous projectiles.
A dull blade is more likely to snag and thrust (kickback).
Inspect the blade regularly, and do not operate the trimmer
with a dull, worn, or damaged blade.
NORMAL
BENT
A dull blade can be sharpened, but a blade that is worn out, bent,
cracked, chipped, or otherwise damaged must be replaced.
When a blade needs sharping or replacement, take the trimmer to a
Honda trimmer servicing dealer. Or, if you have a torque wrench, you
can remove and install a blade yourself.
OUTPUT SHAFT
(left-hand thread)
WORN
CRACKED