The ornamental design for a spoolcap and threadbobbin holder, combined as shown and described.
FIG. 1 is a top perspective view of a spool cap and thread bobbin holder combined shown in condition of being assembled with a spool;
FIG. 2 is a bottom perspective thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a side view thereof; and,
FIG. 5 is a bottom view thereof.
In FIG. 1, the broken lines connecting the centers of the separated components are included to show the order of assembly, and the broken lines depicting the spool represent unclaimed environment. The other broken lines in the drawings views are included for the purposes of illustrating portions of the spool cap and thread bobbin combined that form no part of the claimed design. None of the broken lines form a part of the claimed design.