Four Line Trimmer Head How to Match the 6 Hole Plate

When choosing a four line trimmer head, the first thing to look at is not the thread, but the six holes on the top plate. The 40-4 is a four line head: a white top plate with six holes around the center, a black base, and four lines coming out in four directions. Those six holes are the mounting holes. The head bolts onto the gearbox through them, so the hole count and hole spacing must match the old head, no matter how well the thread fits.

Why does one cutter run four lines instead of two? More lines give a wider working cut per revolution, so thick or weedy ground is cleared in fewer passes. The four lines leave from four directions, and if one breaks, three keep cutting. The price is that a four line head eats line faster than a two line head.

How do you fit it? Feed the line into the spool channel, pull the four lines out of the four exits, line the six holes with the gearbox screws, tighten, and cut all four lines to the same length. The head is a consumable, so replace it when the exits wear loose or the plate is dented.

For heavy brush and weedy ground, a four line head means fewer passes. Six hole flange cutters and brush cutters mostly take this 40-4, but check the old head's hole spacing and thread before ordering, or send a photo to confirm.