The coupling apparatus includes a gear shaft, including a sun gear at one shaft end for connecting to a reduction gear box. The sun gear drives a planetary gear train inside the gearbox. The coupling apparatus has outer splines on the gear shaft other end that mesh with inner splines of a ring gear connected to a coupling flange member by bolts and nuts. The flange member transmits high torque from a high speed turbine shaft to the gear shaft through the intermeshed splines. The teeth of the inner and outer splines are kept lubricated from a stationary spray source on the turbine side via an oil catcher mounted on the flange member opposed to the ring gear. The flow of lubricating oil during operation is from the oil catcher, through holes in the flange member, and to the intermeshed splines. Both oil catcher and ring gear are centered by a rim positioned on the flange member.