These bricks could originate in two different molds, but because they are found together in Modulex colors it looks like they have a common origin. This mold seems to be made from a combination of previous molds.
Logo: Modern logo
Inner ribs: none
Inner tubes: with rounded bottom
Flowrib / center line inside top surface: Yes.
Previous mold numbers under the flowrib on the bricks with the I inside the tube show that this mold reused parts of a previous mold. The design with the mold pip on the short side and flowrib was probably introduced in 1968. It replaced the earlier design with the mold pip on the bottom edge. On all the bricks I have seen the number below the flowrib matches the number inside the tube. This is not unique to this mold.
Mold pip: just above the center on the short side.
Mold numbers: I
Two versions exist:
- Above left tube numbers 1 to 9 (9 bricks)
- Inside left tube: numbers 10 to 20 (11 bricks)
With the pat.pend mark in upright position, except for nr 1 and 15.
Numbers 11, 12 and 14 to 20 show the (matching) mold numbering of a previous mold below the flowrib. I suspect this was a “1958 design” with a number on the short side but no mold identification letter. The number engraving of the number 12 has the 2 over a previous 1, so it should be possible to identify that earlier mold. I might have seen it before…
Intellectual property protection: Pat. pend.
Found in the “LEGO-logo” Modulex colors (1963-1968).
- 2 Grey (matches Light Gray)
- 3 Black (a more charcoal shade)
- 4 Terracotta
- 5 Buff (matches Tan)
- 6 Ochre yellow
- 7 Olive Green
- 8 Teal blue
- 9 Brown
- “light gray”, made from a different material.
and in the regular LEGO System colors
- 21 Red
- 23 Blue
- 26 Black (the common color)
I have found red, blue and black with Modulex-color test bricks and a single red brick with regular production bricks.
Transparent (Modulex 0, LEGO 40), white (Modulex 1, LEGO 1) and yellow (LEGO 24) are still missing, but looking at the other colors, I assume that they were made.
- Found in Modulex colors
[Original post and comments on Flickr.]