Some cleaning required 🙂
According to the record of the 1988 court case Interlego AG v Tyco Industries Inc the design with a flowrib was drawn in 1968.
(…) The matter is best exemplified by reference to the 2×4 brick, the basic design of which was produced in 1968 and is represented by a drawing number 300100 dated 4th March 1968. That contains five images, that is to say, (1) a depiction of the underside of the brick showing the walls of the skirt, the tubes and a “flow-rib” rendered necessary by the shape of the moulds then used in manufacture; (2) a cross-section of the side-view of the brick showing the knobs on top, the walls of the skirt at each end and the walls of the tubes (3) a cross-section of the end view, showing the side-walls of the skirt, the tube and the knobs; (4) a depiction of the top of the brick showing the outline of the eight knobs and (5) a representation of the side view of the brick not in cross-section. The first four of these are to a scale of 2 to 1 but the fifth is drawn to the actual size of the brick apparently for the purpose of enabling the design to be easily identified by those unskilled in reading technical drawings. In each case, save the last two, dimensions and design tolerances are indicated by figures and arrows.
The primary facts are not in dispute. This drawing formed the design for bricks manufactured up to 1971 or 1972. At that time Lego involved a new design with a thinner wall and re-drew their drawing showing thinner walls, a split in the tubes, ribs on the inner walls to provide co-operation with the existing range of bricks and no flow-rib. (…)
There seem to be a HUGE amount of bricks with the mold pip on the short side and a flowrib. Initially, the molds were numbered with a letter (using the Danish alphabet) and a cavity identification number (1 to 24). Different mold identifications, like bricks using numbers instead of letters, were also made.
The main reason many of these bricks are missing from my photostream is because they are incredibly difficult to sort. It looks like many of the letters were used in at least 5 molds, and there could be more…. This photo shows five versions of a “mold C, position 3” brick.
If these molds were really all made in the 1968-1972 time period, I am astonished by the amount of molds needed. Five times the alphabet (minus a few letters, plus a few other mold numberings) could mean that somewhere around 125 different molds producing 24 bricks each were made in these few years only…
[Original post and comments on Flickr.]