October 2004 and June 2006 ARB application guide North American Version both list the specs as follows.

Part #, Free Hight, # Coils, lbf/in spring rate, (application)

OME912, 420 mm, 10.8, 180-300 (medium load Trooper 92-02)
OME913, 390 mm, 9.3, 180-300 (medium Amigo/Rodeo 5door coil spring 98-02)
OME919, 430 mm, 10.8, 200-280 (heavy load Trooper 92-02)

bar diameter is same for each. 913 has lowest coil weight, 912 is + 0.8Kg and 919 is + 0.9Kg.

I verified the application guide is correct as it pertains to the OME912 and OME913 part numbers with a Rep at ARB-USA who cross checked for any updates.
I also cross checked in the Oct 2005 International Application guide and the specs are identical number for number, only the applications are listed as follows;

OME912 (medium load GM Frontera 95-98) and (medium Jackaroo/Monterey 92-2/2001)
OME913 (medium load GM Frontera 99+ 5 door)
OME919 (medium Jackaroo/Monterey 3/2001 - 04, Heavy load Jackaroo/Monterey 92-2/2001)

hope this information is helpful and clears up any confusion about the specs.