What is the viscosity of mobil shc 634 synthetic oil?

The viscosity is 161. ';Mobil SHC 634 (ISO 460) synthetic gear oil is the ultimate worm drive gearbox lubricant. SHC 634 will greatly extend worm gearbox life. The gearbox will run cooler, easier, with reduced power loss. Sold in 5 gallon pails.';