These bricks have been on my lists since maxx3001 mentioned them years ago, and last week I finally got a chance to see them. I even got the opportunity to trade one! Thanks!
Logo: Modern logo on the studs
Inner ribs: none
Inner tubes: with rounded bottom
Flowrib / center line inside top surface: Yes.
Mold pip: on the short side
- (F1 The A is engraved over an earlier 1 or 7)
- F3 The C brick has an additional inverted C below the right tube
Only numbers F2, F3 and F4 have been found. They are identical to one of the 2xABCD test molds.
Intellectual property protection: Pat. pend
(“Pat.” above the middle tube, “pend” below the middle tube.)
- Test brick, not for regular production.
- Identical to the 2xABCD bricks with mold identification letter F inside.
- Mold flash
- Mold damage on top of the brick
Colors known: I didn’t write these down, but I know yellow, blue and light gray.
- When were these bricks made?
- Where were these bricks made?
- Why was the stud logo changed?
There is some mold flash on the bricks with the LEGO logo.
This suggests that the retooled mold did not fit as perfectly as the version with the double ABCD letters on the studs.
Detail of mold damage on top of the F4 brick.
The Borg-Warner Amsterdam G bricks have similar damage on top.
[Original posts and comments on Flickr: mold, mold flash, mold damage.]