The ornamental design for a portion of a buckle, as shown and described.
1. Portion of a Buckle
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Right
1.5 : Top
1.6 : Bottom
1.7 : End view cut at middle portion
The broken lines are for the purpose of illustrating the unclaimed portion of a buckle which form no part of the claimed designs; the dot and dashed lines shown in design 1 are boundaries between the claimed portion and the non-claimed portion; the parallel thin lines (shading lines) shown on the surface of the buckles are used to specify a three dimensional shape of the claimed portion of a buckle.