Abstract: Seam forming apparatus for assembling flexible expansion joint systems of the type used in bridges and roadways and often referred to as strip seals. The expansion joint systems generally include a pair of rigid rails each of which has an involute channel formed therein and a flexible seal gland which is disposed between the rails. The seal gland includes a compressible head section formed along each of its edges which is adapted for being received in the involute channels to form an interlocking seam therewith. The apparatus of the invention includes a rotatable disc having a plurality of spaced-apart teeth about its circumference, the teeth being adapted for engaging a short portion of a shoulder defined by the compressible head. Pushing means are provided which permit the operator of the apparatus to force a short portion of the compressible head into position in the involute channel, thus forming a short portion of the interlocking seam.