Toy building set element

FIG. 1 is a top perspective view of my design for a toy building set element;

FIG. 2 is a bottom perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a top plan view thereof.

The broken lines represent portions of the design that form no part of the claim.