FITS MOST PLASTIC SINGLE ELECTRICAL GANG BOXES SOLD AT HOME IMPROVEMENT STORES. 

 

However, it does not fit the Carlon 1-Gang 22 cu. in. box.  This lid does perfectly fit the Carlon 1-Gang 18 & 20 cu. in. new work PVC boxes. This lid also works on all thin-walled plastic Cantex new work 1-gang boxes as well as several other brands sold at home improvement stores.