The ornamental design for a threadingchair, as shown and described.
FIG. 1 is a perspective view of a threading chair in accordance with my design;
FIG. 2 is a perspective view of the threading chair of FIG. 1 in a reclined position;
FIG. 3 is a front elevational view of the threading chair shown in FIG. 1;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a left side elevational view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines in the drawings including illustration of the pedestal and the reclining and height adjusting mechanisms depict portions of the threading chair that form no part of the claimed design.