I bought a Bosch strimmer a couple of years ago - it is a Bosch 3600H78G71 "EasyTrim". There is now no nylon fibre line (which is the bit used for cutting grass) protruding from the spinning part at the bottom. I presume this is because it has all been worn off (please correct me if I'm wrong, but I believe that these lines are designed to wear off after a while and be replaced by more of the nylon fibre line inside).

The thing is, I can't seem to find much on the web about replacing this nylon fibre line. Do I really have to buy a whole new strimmer because of this? Apart from this, the thing works fine. What I want is just to install a new nylon fibre line for cutting.

I have tried taking the mechanism apart, and the housing for the fibre line has this notch in it: enter image description here

Does this look broken? I have tried feeding the wire through as the instruction booklet says: enter image description here

But every time I try to use the strimmer, the thread seems to break inside the spool; there is no thread coming out of the hole, so it looks like it is being cut at that notch in the white housing (weird, because it's not sharp; I tried pulling the thread against it hard and it didn't break).

The insturction manual obviously shows this as a horizontal slit so the vertical slit that is there, could that be something that has developed over time with use? And could that be what is causing the thread to snap internally each time I use the strimmer (it happens almost immediately when I try to cut some grass)?

UPDATE: I tried again and the thread didn't break at the spool this time, but interestingly, the thread seems to be breaking very easily. Although I can't break it just by pulling it with my hands, almost every time I cut some grass or something with it, I hear the pitch of the motor change up, indicating that the thread has snapped and sure enough, it is significantly shorter than it was when it had been cut by the blade; about half the length, usually. I'm wondering whether the thread material has become "brittle" or weak in some way that makes it unable to withstand cutting things without snapping.

2 Answers 2


If you consult the manual, you find that the part the line comes out of comes apart to expose a bobbin inside of the housing.

You need to find out what the recommended diameter of the line is for the trimmer and get a spool of replacement line.

Hand rewind the bobbin in the proper direction, usually they have an arrow on them to tell you this. Poke the tail out of the hole in the housing when you insert the bobbin, allow about six inches, clip the lid back in place, fasten per manual directions and proceed to use.

enter image description here

  • Hey thanks... I unded the spool holder and there was a load of wire still in there; it must have gotten stuck somehow. One thing I don't get is why that pole in the middle (13) pushes in; it doesn't seem to do anything. The way to unscrew the housing is just to unscrew it VERY hard counter-clockwise - pushing that pole in doesn't seem to make any difference!
    – Jez
    Commented Apr 21, 2014 at 23:02
  • If there's enough string on the bobbin, pull a tail out long enough to hit the cutter blade (18). The "pole" (13) in the middle is how you get it to feed more string off the bobbin. While the trimmer is powered up, you bump it against the ground a couple times and it (13) pushes in to allow the bobbin to turn and feed out the line till you hear it hit the blade (18). Basically when it gets to half length, bump it while spinning. Occasionally, if the bobbin's not wound right, the line can get stuck and not feed out properly, also happens if you let the string get too short. Commented Apr 22, 2014 at 0:07
  • Oh wow, I didn't even know about the blade thing, lol. :-) I'm so getting a lesson in how to use a strimmer here. Adding to favourites.
    – Jez
    Commented Apr 22, 2014 at 0:32
  • Heh, couple decades of running these things. My first job was irrigation on a dairy. The two-cylinder Green Machine had a two step cartridge that fed out what looked like solid nylon rope and would take out Himalaya blackberry canes an inch thick and cut an 18" semicircle swath. Good ditch cleaner. I love my Black&Decker 36V Li-ion, only thing better would be a Stihl. No stink, no gasoline mix, no cord. Only the noise of grass getting ripped to shreds. Commented Apr 22, 2014 at 1:23
  • Please see the update to my question; I tried to fix the spool and the thread keeps breaking each time I try to use the strimmer.
    – Jez
    Commented Apr 22, 2014 at 14:22

A lot of people recommend soaking the trimmer line in water for a couple of days so that it's more pliable and breaks less. I've even seen it recommended from manufacturers of trimmer and trimmer line. Some lawn professionals I've seen buy a big spool of line and keep it in a 5 gallon bucket of water all the time. Nylon is hygroscopic and does absorb water. Try soaking the line for a couple of days to see if it breaks less.

From what I've seen of your trimmer you buy replacement cartridges with spool and line already wound on it rather than buying separate line and winding the spool. You may be able to buy the same thickness of line in bulk and rewind the spools yourself to save some money.

  • 1
    I had issues with my line breaking like crazy. I didn't soak the line, but I spray the line with WD40 once its spooled up. I have not broke a single line since.
    – Evil Elf
    Commented Jul 28, 2015 at 12:20

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