Most likely a manufacturer abbreviation. Unable to determine what company if this is indeed what that is. The initials CSTK have no meaning to weight or alloy content as far as we know.
Silicone 1000 cStk refers to silicone fluid with a viscosity of 1000 centistokes. It is a type of silicone oil that is often used in various industrial applications due to its lubricating and insulating properties.
The abbreviation for centistoke is "cSt." It is commonly used to measure the viscosity of fluids.