Abstract: To secure an assembling of two boards against displacement in one direction the assembling plug is worked out as a body (1) having a cross section increasing from a central portion (2) to both sides. The body (1) is placed in corresponding recesses in the two boards so that the central portion (2) is co-extensive with the tangent surfaces of the two boards. The body may have conical faces (4) with planes (4') tangent to these. FIG. 1.