So I'm about to service the ZXR forks and I'd previously seen mention of people using Dexron III automatic transmission fluid in forks which required about a 7wt oil. There seem to be two oil weights floating about SAE and Non SAE which seems to be 1.5x SAE weight, so SAE 5 = non-SAE 7.5 - numbers from the penrite spec sheets. Why would I bother with the effort when I can just get fork oil - well ZXR specifies 5wt, though I had encountered somewhere mention of people going slightly higher with a mix of 5wt and 10wt - that's two litres at ~$25/litre. So I did some digging and some reading and hit some good pages. First promising link was this one, there is some great information on this page - https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=466621 It mentions both ATF and ISO graded hydraulic fluids as well as the important VI - viscosity index for heat stable fluids. One poster also gives some target oil viscosities for various situations - please note that he provides ISO grades in the numbers below - not SAE weights. Generally MX bikes need a very fast acting fluid usually in the 16-28 range, big fat enduros like your KLR and my XR around 22-32, street sport 32-46, 46+ for the big bikes. Tractor hyd fluid is usually around a 46-52, ATF 32-38, SAE 10 engine oil 46ish. Engine oils make very poor suspension fluids. That info is very useful for anyone with access to tractor or industrial machine hydraulic fluids in various grades for mixing and matching. So with some starting points on what the poster claimed were the oil weights I came across this page with the cross reference weights and other aspects - notably viscosity measurements in centistokes and viscosity index numbers - lots of specific details on how the actual measurements are made. http://www.machinerylubrication.com/Read/411/oil-viscosity OK so now I have a clue about what I'm looking for in specs. Easy search gives me data sheets on two ATF's Mobil 1 ATF and Valvoline Dex III available from Woolworths of all places - nice to know in a pinch I could get some ATF from Woolies if I needed SAE-10wt/ non-SAE 15 fork oil and the numbers are very good on the Valvoline. Mobil 1 Synthetic https://www.mobil.com/english-us/passenger-vehicle-lube/pds/glxxmobil-1-synthetic-atf Viscosity, cSt (ASTM D445) @ 40 ºC 36.3 @ 100 ºC 7.4 Viscosity Index 176 Valvoline Dex III https://go.lupinsys.com/valvoline/h...92730caff909/search_api/ATF_DX_3-PI_Sheet.pdf Viscosity, cSt (ASTM D445) @ 40 ºC 34.1 @ 100 ºC 7.1 Viscosity Index 175 Also two Penrite fork oils 5wt & 10wt, which as luck would have it went on special the end of last week at Supercheap so I grabbed one of each. Makes this slightly redundant for the short term, but it's info worth sharing. Penrite 5wt - Full Synthetic - spec sheet says covers - Fork Oil Grade 7.5 (Non SAE) Fork Oil SAE Grade 5 https://www.penriteoil.com.au/assets/pis_pdfs/MC FORK OIL 5 (FULL SYNTHETIC).pdf Viscosity, cSt @ 40 ºC 20.0 @ 100 ºC 5.0 Viscosity Index 193 Penrite 10wt - Full Synthetic - spec sheet says covers Fork oil grade 15 (Non SAE) Fork Oil SAE Grade 10 https://www.penriteoil.com.au/assets/pis_pdfs/MC FORK OIL 10 (FULL SYNTHETIC).pdf Viscosity, cSt @ 40 ºC 37.9 @ 100 ºC 7.5 Viscosity Index 174 So in conclusion a Penrite 10wt full synthetic is amazingly close to an ATF fluid - perfect substitute. For anyone with access to ISO graded hydraulic fluid you've also now got some good starting points for conversion to SAE weight fork oils.