I claim the ornamental design for a pen using a tire valve-stem cap, as shown and described.
FIG. 1 is a side elevation view of a pen using a tire-valve stem cap, showing my new design, the opposite side elevational view being identical to that shown;
FIG. 2 is a top plan view thereof; and,
FIG. 3 is a bottom plan view thereof.
The broken line showing of the words “Logo Here” is for illustrative purposes only and forms no part of the claimed design.