Here is a picture of the markings on the top. Notice on the right is the rare catalog number in the center of the marking,5013. The other two later production markings have the recessed embossed Square D Co. logo in the center but if you look closely at the marked pieces you may have you can usually see the 5 to the left of the center logo and part of the 3. All the ones I have seen are like this. I have one small strain insulator with the Square D Co Peru Ind marking and it has a catalog number 5500 embossed on it and a re embossed logo on the other end.