c. 1950s. 3.25x4.25" original fold-over Bols Mfg. Co. mailer w/"Greetings From Hopalong Cassidy" return address. Back of mailer shows picture of Hoppy and image of Hopalong-Aid drink mix packet. Extensive text lists flavors and price. Mailer is lightly aged but Exc. Mailer contains complete set of 12 glossy 3x4" photo cards w/facsimile signatures. Set is complete. Cards have some tiny corner bumps but are o/w NM. Rare and only the third set we've offered in our 48 years.