The ornamental design for billiard cue shaft, as shown and described.
FIG. 1 is a side view of the billiard cue shaft;
FIG. 2 is an enlarged top plan view thereof;
FIG. 3 is a bottom plan view of FIG. 2;
FIG. 4 is a left side elevational view of FIG. 2;
FIG. 5 is a right side elevational view of FIG. 2;
FIG. 6 is a cross sectional view taken on line 6-6 of FIG. 5
FIG. 7 is an enlarged fragmented bottom plan view taken FIG. 3;
FIG. 8 is an enlarged fragmented right side view taken on FIG. 5; and,
FIG. 9 is an enlarged cross sectional view taken on line 9-9 of FIG. 6.
The broken line showing of a portion of the billiard cue as well as the circle areas of FIGS. 7 and 8 is included for the purpose of illustrating and forms no part of the claimed design.