A spread swap 3-leg strip (sss) is simply a strip of Spread Swap 3-Leg , each of which is always set to a calendar month.
Once you have defined the strip, you can then see more information on the underlying spread swap 3-leg instruments in the Expiry Dates & Rates Window (accessed by clicking the Expiry Dates & Rates button).
Pricing a spread swap 3-leg strip in SDX Commodities & Energy
The spread swap 3-leg strip (sss3) is currently only supported in the Portfolio page.