from thier site
Recommendations
AMSOIL Shock Therapy Suspension Fluid is recommended for front forks and shocks in snowmobiles, motocross and cruiser motorcycles, ATV's and other racing and recreational use vehicles. Two different formulations are available: The lightweight grade (STL) is recommended, but not limited to, Showa, Kayaba, Bilstein, RydeFX, Penske, WP forks, RACETECH (US1) and Custom Axis suspension systems that demand quick rebounds under extreme hot and cold weather applications, while the medium grade (STM) can be used in Ohlin, FOX, RACETECH (US2), Koni, WP shocks and Harley-Davidson forks that recommend type "E" or "B" fork oils, as well as other applications that require more dampening and slower rebounds. Refer to the owner's manual for individual capacities, proper disassembly and further recommendations. Owner's manuals may refer to weights when recommending suspension oil. These weight numbers are arbitrary because no industry standard exists for classifying suspension oil. The numbers can range from 2.5 to 30, depending on the manufacturer. AMSOIL STL correlates closely to a 5 weight, while AMSOIL STM is close to a 10 weight.
Compatibility
AMSOIL STL and STM can be mixed together based on individual requirements and applications, and they are compatible with most other suspension fluids.