Abstract: A filament-type trimmer comprises at least one filament spool carried by a rotary housing driven by a motor the speed of which increases with decrease in load. Means for normally restraining rotation of the filament spool relative to the casing is responsive to centrifugal force to release the spool to feed additional filament when the speed of the motor increases due to a decrease in load by reason of the extending end of the filament having become shorter by wearing or breaking off. In one embodiment the feed of additional filament is delayed until by manual control the speed is reduced below normal operating speed.