i was actually using tectite fittings not a sharkbite fittings (they look very similar) , i had a pin hold leak in the copper pipe coming out of the water heater, its 3/4 inch diameter copper. so i cut that section out then i added more pex pipe 3/4 inch to be joined to the copper done by a tectite fitting
its called a female sweat adapter (sweat indicating soldering, but this is a solder free adapter because its not always save to use the torch to sweat solder a pipe)
you get absolute shit directions on the tectite fitting though