View on LOZ Suggested Retail: $89. ZINUS 7 Inch Metal Smart Box Spring / Mattress Foundation / Strong Metal Frame / Easy Assembly, Twin. Unlike a traditional box spring, the Smart box spring is made of solid steel. Durable steel is used to construct the inside framework of this foundation; twin size supports a maximum weight capacity of 350 lbs., while all other sizes can support up to 700 lbs. All parts, tools and instructions are packed into one compact box that ships straight to your door Box spring only, a bed frame or platform bed is required to support this foundation and is sold separately. Fast, easy assembly with no tools.. 7 CALENDAR DAY FULL REFUND GUARANTEE ON THIS ITEM IF ANY ISSUE IS FOUND THAT WAS NOT DESCRIBED/PICTURED. 7 CALENDAR DAY STORAGE IS ALSO AVAILABLE. SEE NOTES TO BIDDER, IN AUCTION DETAILS, AT THE TOP OF PAGE 1 FOR MORE INFO.