This 3/4"x10 brass castle nut is used on all 1" diameter shafts (remember the shaft is tapered at the prop). 1" shafts were used on all inboard equipped Catalinas with the exception of the Catalina 250 (which uses a sail drive) and a Catalina 42 (which uses a 1-1/4" shaft). A 1/4" square key and a cotter pin are also included.
Just a note of interest... Although mild steel and hardened steel castle nuts are readily available, brass castle nuts are not. They must be individually machined for us from a heavy profile, commercial brass nut, hence the surprising cost for a single nut.