The cards in this 340-card set measure approximately 2 5/8" by 3 3/4". Following up with another horizontally oriented card in 1956, Topps improved the format by layering the color "head" shot onto an actual action sequence involving the player. Cards 1 to 180 come with either white or gray backs: in the 1 to 100 sequence gray backs are less common and in the 101 to 180 sequence white backs are less common. The team cards, used for the first time in a regular set by Topps, are found dated 1955, or undated, with the team name appearing on either side. The dated team cards in the first series were not printed on the gray stock. The two unnumbered checklist cards are highly prized (must be unmarked to qualify as excellent or mint). The complete set price below does not include the unnumbered checklist cards or any of the variations. The set was issued in one-card penny packs or six-card nickel packs. The six card nickel packs came 24 to a box with 24 boxes in a case while the once cent packs came 120 to a box. Both types of packs included a piece of bubble gum. Promotional three card strips were issued for this set. Among those strips were one featuring Johnny O'Brien/Harvey Haddix and Frank House. The key Rookie Cards in this set are Walt Alston, Luis Aparicio, and Roger Craig. There are ten double-printed cards in the first series as evidenced by the discovery of an uncut sheet of 110 cards (10 by 11); these DP's are listed below.