Woosung/Zebec make brass oar mount inserts for NRS size pipe inside diameter (sold by Star Inflatables, KVI rafts, etc.. This is what I have on both my raft frames. I get them from Doug at KVI.
the Zebec oar mount insert used on a piece of NRS pipe with an NRS lopro to attach to the side rail with the orientation of the Zebec brass oar mount tipped outward:
click image for a much larger size to zoom in.
Zebec brass insert used with NRS pipe and the Zebec oar mount side rail frame fitting with the brass insert tipped inward:
Doug at KVI: