Mail processing plants used four-sided plastic letter trays, such as this, in the 1970s, 80s and 90s for both manual and mechanized letter mail sortation. The tray is made of solid, crack- and shatter-resistant plastic and has red directional arrows painted on either long side with raised "1/4" and "1/2" red markers on its floor. Handholds at either end, imprinted in the mold with "Property of U. S. Post Office Department," facilitate manual handling. One side of this tray is stamped in black ink “DI Corp. / Anniston, Alabama / 1980 May / USPS Contract No. 104230-80-V-0660 / USPS Item No. 1254 / Material: PPO.” The tray is 26 inches long, 12-5/8 inches wide, 4 inches deep and weighs 4 pounds. Its capacity is 20 pounds or the equivalent of 2 feet of letter mail.
The plastic tray is well suited for mail preparation, mail transport and mail staging because of its large capacity, deep sidewalls, and its ability to remain stable and stackable when full. Letter mail is unbanded, faced, and placed vertically — with the stamp away from the handler in the trays. Full trays are moved to the LSM (Letter Sorting Machine) or manual distribution areas. Used primarily in the processing plant, such trays were also loaned to mailers for mail preparation.