in the particular embodiment of the inventive combustion assembly 110 shown in fig5 exterior threads 124 provided on the venturi divergent section 122 mate with interior threads 126 provided in burner tip 120 however it will be understood that a welded connection or other suitable attachment could alternatively be used in inventive combustion assembly 110 combustion tip 120 preferably includes an interior shoulder 125 positioned forwardly of the combustion tip interior threads 126 when combustion tip 120 is secured on venturi mixer 115 the forward end 127 of the venturi divergent section 122 preferably abuts the combustion tip interior shoulder 125 in addition the inside diameter 128 of combustion tip 120 at interior shoulder 125 is preferably substantially equal to the inside diameter 130 of the venturi divergent section 122 at its forward end 127 thus a smooth transition from the venturi divergent section 122 to the burner tip 120 is provided although the inventive structures shown in fig3 5 are preferred it will be understood that in each of embodiments 55 90 and 110 the attachment between the venturi mixer and the combustion tip could be reversed such that the rearward end of the combustion tip and or an extension thereof having a rearwardly convergent i e forwardly divergent interior wall is received in the.