Abstract: An assembly for a catalytic converter includes a housing and a catalyst-supporting substrate, or monolith. The housing includes upper and lower halves. One of the housing halves includes an enlarged perimetrally extending lip region. The other housing half includes a perimetrally extending insertion portion for insertion into engagement with the lip region. The housing halves are compression-loaded one within the other to either a predetermined force or a predetermined depth of insertion. This shoebox-like assembly is fabricated by supporting the lower housing half on a perimetrally extending ridge formed in the lower housing half and applying force to a perimetrally extending ridge formed in the upper housing half until the predetermined force has been reached or the insertion portion has reached a predetermined depth of insertion within the lip region. The assembly is compact and utilizes a minimum of space on a vehicle.