Abstract: A first elongated steel frame has a dowel mounted thereon at right angles. The dowel projects through an aperture in a compressible filler board thence through a registering opening in a second elongated steel frame. The long dimensions of the two frames are parallel and each frame abuts an opposite surface of the filler board. A cap-like shield covers the free end of the dowel with end clearance to accommodate longitudinal thermal expansion and contraction. The two steel frames are free to move toward and away from each other but are constrained to move in unison in a direction perpendicular to the dowel. By bonding each frame to a respective concrete slab of a pair of adjoining slabs with the filler board co-planar with the joint, the slabs partake of the same freedom of motion in one direction and the same restraint in the other two directions.