These bricks can be found in the USA. Initially, they were made with the Narrow straight O inside circle logo in upright position. On some later bricks rotated logos can be found. Even later, they have been replaced by the Samsonite open O logo. Unlike the 1×6 and 1×8 bricks, no mixed logo bricks have been found yet.
Logo: Narrow straight O inside circle, Samsonite open O
Material: CA
Wall type: Thick
Inner ribs: none
Inner tubes: with rounded bottom
Flowrib / center line inside top surface: No
Mold pip: corner bottom edge
Mold identification letter: large P
Mold position numbers: 1 to 20. There is one brick without number. It must have been position 18.
Intellectual property protection: Pat pend above and below right tube
Colors known: red, white, yellow.
Remarkable features:
- Location of pat pend mark
- Can be found with different stud logos
Unanswered questions:
- When did the logo change?
[Original post and comments on Flickr.]