How do you measure your weedeater? 12 in -13 in -16 in. So confusing. What do I need??

I wasn't aware string trimmers came in widths. I paid no attention to any dimension when I purchased the one I have. 

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Move your question to Home & Garden<Garden & Landscape as it's currently in Health>Diet & Fitness and not applicable to this subcategory (and thus decreases your chances of getting many useful answers).

You can move your question by clicking Edit (pencil icon for mobile)>Edit category just beneath your question, then selecting the category in which it is better suited.

You don't need to measure it, just use it!