Inner ribs: none
Inner tubes: with rounded bottom
Flowrib / center line inside top surface: Yes.
Mold pip: on the short side, below the letters on the studs.
- A F1 The A is engraved over an earlier 1 or 7
- B F2
- C F3 The C brick has an additional inverted C below the right tube
- D F4
Intellectual property protection: Pat. pend
(“Pat.” above the middle tube, “pend” below the middle tube.)
- Test brick, not for regular production.
- A small capital letter on the top right and bottom left studs, the other studs are blank.
- The font size is identical to that on the bricks with a letter in the top right corner. There are slight differences in the position of the letter so it does not look like one mold was changed into the other.
- Very similar to the 2xABCD bricks with mold identification letter D inside.
Colors known: many.
- When were these bricks made?
- Where were these bricks made?
[Original post and comments on Flickr.]