An "oil sock" is not a standard term used in the context of motorcycles or Harley-Davidson Sportsters. It is possible that you may be referring to an aftermarket accessory or a slang term that is not widely recognized.
Harley-Davidson Sportsters, like many other motorcycles, have an oil reservoir or oil tank that stores the engine oil. This oil is circulated through the engine to provide lubrication to various components and ensure smooth operation.
To better assist you, please provide more information or clarify what you specifically mean by an "oil sock" or the context in which you encountered the term.