Abstract: A plurality of tubes having flanged ends are assembled in end to end fashion by clamping the flanges between first and second portions of connector blocks, the portions of the connector blocks being provided with channels formed in the opposed surfaces thereof for defining a passage through the connector block when assembled to each other and a groove in the channel formed in the opposed surfaces for receiving the flanges formed around the ends of the tubes. Each of the portions of the connector blocks is provided with complementary projections and recesses for frictionally engaging one portion to the other and for frictionally engaging the connector blocks to the pieces of a multiple piece, snap-together, children's building toy set.