A screed bar for a vibratory concrete screed is formed from a long hollow extrusion having generally flat enclosing walls and defining in cross section two triangular sections that share a common interior wall. As such, the frame of the hack-saw can be used as a conventional L-square. The interchange includes a common format processor and a plurality of converters to interface with a plurality of different controllers of mobile communications. The riser reactor is an external riser reactor with a curve andor low velocity zone at its termination and wherein a part of the catalytic cracking catalyst has deposited in the curve andor low velocity zone. The reaction occurs between the pendant siloxane groups and the vinyl or ethynyl groups.