Sidearm fittings for gas handling can be used to provide gases into larger Spinner Flasks with vertical sidearms during cell culture to enhance the productivity of the cell culture. Together with sensor probe fittings and media handling fittings, they allow Spinner Flasks to operate as bioreactors when they are attached to appropriate cell culture controllers at costs considerably below those of traditional bioreactor vessels with expensive stainless steel headplates. The fittings are comprised of a PET insert with a fluorocarbon O-ring and a 45mm polypropylene sealing cap. Stainless steel tubes are held in place by modified polyphenylene oxide thermoplastic nuts with integrated ferrules. The fittings are completely autoclavable. Sidearm fittings for gas handling can be used to provide gases into larger Spinner Flasks with vertical sidearms during cell culture to enhance the productivity of the cell culture. Together with sensor probe fittings and media handling fittings, they allow Spinner Flasks to operate as bioreactors when they are attached to appropriate cell culture controllers at costs considerably below those of traditional bioreactor vessels with expensive stainless steel headplates. The fittings are comprised of a PET insert with a fluorocarbon O-ring and a 45mm polypropylene sealing cap. Stainless steel tubes are held in place by modified polyphenylene oxide thermoplastic nuts with integrated ferrules. The fittings are completely autoclavable.