The ornamental design for a reel for metalwire, as shown and described.
1.1 : Perspective view 1
1.2 : Perspective view 2
1.3 : Partial enlarged perspective view of 1.2
1.4 : Front
1.5 : Back
1.6 : Top
1.7 : Bottom
1.8 : Left
1.9 : Right
The thin lines in the representations represent contours only and do not illustrate an ornamentation or decoration on the surface of the product; the parts shown by means of broken lines in the reproductions of design 1 are not part of the claimed design; the dotted-dashed lines in the reproductions of design 1 show only the boundary between the part of the claimed design and the other part.