No matter.
The bigger the fixation rings - the smaller (and lighter) the diaphragm.

d8r075 have the smallest fixation rings, and is standard in 2404H-1 and 2402/075. Heavier diaphragm: more rugged, and less HF exension.
d16r2405 have bigger fixation rings, and is the standard for 2404H and 2405/077. Lighter diaphragm, more HF extension.