The ornamental design for an adjustable clamp, as shown and described.
The nature and intended use of the article in which the design is embodied is that of an adjustable clamp having jaws that may be tightened against an object with adjustable pressure. The pressure may be adjusted by controlling the amount of squeezing pressure applied to handles of the clamp.
FIG. 1 is a perspective view of an adjustable clamp showing my new design;