Winry wears it everywhere, and she's proud of its imperfections because they're proof that he made it with his own two flesh hands. It becomes her rosary, her time-clock, these grains of sand turned into something beautiful not through alchemy, but through the processes of life and time and the industry of two hands.
She uses her two hands to build him a leg – better than any he has ever had. It's what she's always done whenever he's away, but this time she knows that he can – will – appreciate it.