Detail 01
Sold as one A string
Only the top string. Your other three stay as they are, so age and feel may not match.

Independent shopping perspective
A single A string for violas 15 inches and up. For players replacing a worn top string rather than buying a full set.

Strong match
Consider the trade-offs
What matters in use
Catalog numbers tell only part of the story. These are the details most likely to change how this product feels, sounds, or fits into a setup.
Detail 01
Only the top string. Your other three stay as they are, so age and feel may not match.
Detail 02
Cut for violas with a 15-inch body or larger. Shorter instruments end up with excess winding at the peg.
Detail 03
The highest and most exposed string on a viola. It wears out first, which is why it's sold on its own.
Detail 04
Per-string cost. Replacing all four this way adds up quickly compared to buying a set at once.
Detail 05
Keeping one maker's line on all four strings gives more even tension and response from string to string.
Final check
Product questions
Straight answers to the questions shoppers most often ask about this product.
Yes. The 15+ sizing covers violas from 15 inches of body length upward, which includes 16-inch instruments.
No. This is the A string on its own. You would need to buy the D, G and C separately.
No. Viola string lengths and tuning differ from violin, and it won't sit correctly at the pegbox or tailpiece.
You can, and plenty of players do. Tension and response across the four strings just won't be as even as a matched set.