A riser assembly includes riser segments, each having threaded ends. A coupling nut is connected to the threaded end of the first riser segment. The threads of a second riser segment and a set of corresponding threads of the coupling nut are breech threads, which allow the second riser segment to stab into the coupling nut and engage the first riser segment. The coupling nut rotates a portion of a turn in order for the breech threads of the second riser segment and the first riser segment to engage each other. Castellations on the first and second riser segments engage each other to transmit torsional forces from one riser segment to the other instead of through the threads.