?
Jinhao 75 (image cribbed from an eBay listing):

Parker Sonnet (image taken from Parker's website):

The grip section, nib shape, cap band, clip, and body shape are all exact duplicates. I'm pretty sure the sections are even interchangeable.
The only differences are the nib itself (obviously) and its engravings, and a slight shape change to the top of the cap.