On some trimmers, there is a little divot where you just pry the cap off with your finger. If this is an older whipper snipper or it has been a while since the thread has been changed, the cap will probably stick a bit—you may need to use a bit of pressure. On some newer trimmers, you don’t even take the cap off. You just pull out the old line and feed a new one into it (Ryobi in particular seems fond of this design). There are some minor variations between brands, but the vast majority of lawn trimmer strings are changed the way we’ll outline here. Always refer to your instruction manual for unique instructions.

You may need to cut the wire where it sticks out of the housing if it’s stuck. Use nippers, tin snips, or shears if you need to. Take a mental note of which side of the spool is facing out when you remove it. You can only install it one way normally, but it may make things easier if you remember the orientation now.

If the string isn’t inserted into a loop or opening, there may be a tiny clip that pins that wire against the center of the spool. If there are 2 or 3 different lengths of string, you may need to insert 2 or 3 lengths of string into the openings.

The round wire tends to hold up better than the flat plastic stuff, but whipper snippers aren’t universally compatible with any kind of string. Refer to your manual to determine what kind of wire you can use. Some newer trimmer models sell pre-wound spools you can simply swap out instead of replacing the string (Black and Decker models are the most popular brand that does this). If you have a 2-string trimmer but there’s only one opening for it on the spool, pull the string through the opening until you’ve reached the middle so you have 2 equal haves hanging off the spool.

Do not add so much string that it extends past the rim of the spool. If you have a 2- or 3-line trimmer, roll the wire evenly around each of the individual sections (a 2-line trimmer will have 2 slots, and a 3-line trimmer will have 3 slots).

On some trimmers, you can lock the spool in place by pressing on tabs or squeezing the spool together until you hear a click.

Remember to orient the spool the same way it was oriented when you removed it! There will typically be a logo or note on the side that’s supposed to face away from the trimmer.

Once the cap is locked, you’re good to go! Your whipper snapper cord will cut and trim like new.