A polymeric connector block for interconnecting a plurality of elongate tubular members into a structure has five-sided front and back sides with an orthogonal pattern of three parallel through-apertures therethrough. A fourth through-aperture passes from the left side to the right side, intersecting two of the parallel through-apertures at 90.degree.. A non-through aperture passes from the top side and intersects the other of the parallel through-apertures at 90.degree.. A sixth aperture extends into the block at an intermediate angle such as 45.degree.. There are no apertures in the bottom side. Tubular members are insertable into the apertures and lockable therein by lockscrews. Tubular members may comprise tubing, pipe, electrical conduit and the like, and may include non-tubular materials such as solid rods. A wide range of structures may be created.