There's a Armstrong wrench with that number that belongs to Caterpillar Tractor Company. There's a 3555A, 3556A, 3557A, 3558A,3559A, 3560A,3561A and 3562A. The only one that I've got in my colllection is 3561A. You a look in P. T. Rathbone's first edition of The History Of Old Time Farm Impelment Companies.