The ornamental design for a plug for use at an end of a tube, as shown and described.
FIG. 1 is a perspective view of the plug for use at an end of a tube;
FIG. 2 is a front view thereof;
FIG. 3 is a plan view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is an enlarged sectional view taken at 6—6 of FIG. 2;
FIG. 7 is an enlarged sectional view taken at 7—7 of FIG. 2;
FIG. 8 is an enlarged sectional view taken at 8—8 of FIG. 3;
FIG. 9 is a reference view of the plug for use at an end of a tube together with a heat exchanger pipe for a steam generator; and,
FIG. 10 is a reference view of the plug for use at an end of a tube together with a heat exchanger pipe for a steam generator, a tube support plate, and a tube plate.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.