yes, a common usage, and the single number ratings are referred to as "straight weight" [and the two-number ones are 'multigrade'
], but as Jerry points out,
the 'W' really means winter, for the cold viscosity rating .... SAE oil standards are different now than when they started, about the 20's-30s, when they were classed as 'regular' premium' and 'super', and the 600W stuff under discussion pre-dates the SAE standards
Bill
