The ornamental design for a magneticbase, as shown and described.
The magnetic base magnetically attaches itself to a ferrous support and can support other structures on itself. For example, a strap, which is shown in dashed lines, can be attached thereto.
FIG. 1 is a perspective view of a magnetic base showing my new design.
FIG. 2 is a left side view thereof, with a strap shown in dashed lines. The right side view is a mirror image thereof.
FIG. 3 is a front view thereof, with the strap shown in dashed lines.
FIG. 4 is a top view thereof.
FIG. 5 is a back view thereof; and,
FIG. 6 is a bottom view thereof.
The broken line showing of the strap is included for the purpose of illustrating environment and forms no part of the claimed design.