A chronology of Lego molds?

Last update: 2 December 2016

Recently, I started selling some of my second-hand lego at bricklink.com. I happened to have bought a batch of second-hand lego with some old parts in it going back to the early 1970s or late 1960s. On BrickLink I noticed there is an interest in these older parts. For example the ones with ‘Pat. pend.’ (Patent pending. Lego applied for patents in different countries as of the late 1950s or earlier) inscribed on the inside, or the ones that have it erased with a small ‘blob’ (after the patents were granted). Also the location of the molding ‘pip’ is apparently telling for the age of the brick and hence of the value of it to Lego collectors.

Such markings are of course very handy to estimate the age of a brick. However, I noticed that there is a more detailed coding scheme in the bricks that seems to identify their respective molds. It consists of letters and numbers in various coding schemes and locations on the bricks. Here are a few examples.

Interestingly, while going through a batch of ‘Pat. Pend.’ 2×3 plates, I noticed a few funny mistakes in the molds. This is one. The other also had the logo upside down, but on a different stud.

It seems interesting to me to have a chronology of the different molds and colors, at least for a number of often-used bricks. There is Ryan Howerter’s Lego color timeline chart (also available as web page), and BrickLink’s Color Guide (here) . Unfortunately for my project, before 1970, there were not many colors and most of these seem to have been present as of 1950. So for these two decades, colors are not very helpful to determine the age of a brick. In the early 1970s a handful of additional colors saw the light of day, and another handful in the late 1970. Then things more or less stabilised until the 1990s and 2000s which saw an explosion of colors.  See also sites like this Flickr album by WRme2 who collects all the color and shape variations in the 2×4 brick. It is an impressive collection but unfortunately provides very little information about the years.

Does anyone know of such a chronology? Would you be interested in having access to it if it existed? Would you be interested in collecting the data?

Meanwhile, read below what I have managed to compile so far…


Known mold characteristics

A few introductory notes

Establishing the age of a brick requires historical investigation into its production. Depending on our sources  (books, archives, testimonies, Lego sets and more) and what they say, we can make estimations. It can get incredibly complicated and detailed: for example not only when, but also where and who produced bricks are relevant issues. There is however a time-logic that makes it terribly hard to know until when a brick from a certain mold was being used.

In general, we may know when certain molds were used to produce bricks. Even when we know when Lego stopped using the molds, it does not mean that the bricks that were produced were not used/sold in sets after that date. After all, it could be that bricks were held in storage for a while. So, the time-logic is that the only thing we can know for sure in case we know exactly when a particular mold is used, is that bricks from that mold were not sold before its use. After a mold was taken out of use, we can only guesstimate that it’s bricks were increasingly less likely to occur in sets. Unless, of course we have reliable sources that claim until when bricks of a certain mold were sold.

This means that if you find a set of which we know that it was only produced in 1970, it should not contain bricks from molds used in 1971 or later. The other way around could certainly be possible.

I am a bit of a historian by education and profession, so I would like to make this overview based on sources. So far, these sources are simply other web-sources made by other people. Sometimes these websites stop to exist. Know that I am keeping copies of the webpages for future reference and checking.

One of the problems of the historian is that different sources give different accounts of what happened and when. For lack of some ‘ground truth’ I will simply outline the differences where I cannot solve the puzzles based on what I found. All help is welcome!

From ? to the present : Mold numbers

At some point in time which I do not know, Lego used numbering systems for its mold. You may find these at the bottom of the brick or in other less visible locations. The systems vary over time in character and shape. It may be just a letter, hidden in the inside of a stud, or a combination of a letter and a number. Recent systems include a year and a part number. Having an overview of the characteristics of these systems would already be a great start to determine the age of a brick. Even better would be to have a chronological overview of the exact numbers and letters.

1954 – late 1990s : 2×4 brick without cross support

An easy-to-spot characteristic of basic bricks is the use of cross supports: little walls on the inside that connect the inner tube to the outer wall. In the 2×4 brick, this only concerns the middle inner tube. One Flickr page reports this construction in a cellulose acetate brick, which the author dates as after 1958 (Source: Flickr ).
According to BrickLink, the 2×4 brick without cross support was used from 1954 until 1990 (Source BrickLink ). According to Rebrickable it was used until 1987 (Source: Rebrickable).

The question then is when the support was introduced. BrickLink does not make this explicit. It just contrasts the newer brick (nr. 3001) to the older brick by saying that the older does not have the supports. However, the 3D image of the newer brick contains no cross supports. This newer brick was introduced in 1980. (Source: BrickLink) However it seems that the cross support in the 2×4 brick was introduced in or around 1985 (see below)

1958 – 1962 : Patent pending and introduction of the inner tubes

In 1958, Lego filed a patent request for the stud-tube technique. It was granted in 1962. During that period bricks were produced with ‘Pat. pend.’ written at the bottom or inside. However, not all bricks had this inscription. (Source www.leggodt.nl )

According to The Sphinx blog which provides an overview of the history of the 2×4 brick, 1958 is also the approximate year the inner tubes were introduced. Until then the bricks were empty ont the inside  (Source: The Sphinx) In view of the previous section, the question arises when exactly the inner tube was introduced: in 1958 or before, and if before, which year?

As of 1962 to ca. 1974: Post patent pending / patent pending obscured

When the patent was acquired, Lego removed the ‘Pat. pend.’ from at least some (and perhaps all ?) of its existing molds and started again using molds without any reference to a patent. (Source: www.leggodt.nl)

The patent-pending and obscured-patent-pending bricks had disappeared by 1974. (Source: The Sphinx )

Ca. 1985 (Re)introduction of the cross support in the 2×4 brick

I was not planning to focus on particular bricks but it seems that the 2×4 brick is getting a lot of attention out here on the internet. One good reason for using it also here as a focus is that it has been around since the early days. Another is that it has a sufficient room for mould numbers and other markings. The 2×4 plate would have the additional advantage that the numbers and markings on the inside are more easy to read since the plate is, you guessed it, far less deep.

In any case, the cross support to the 2×4 brick was introduced in or around 1985. (Source: The Sphinx).

In or before 1990: introduction of the part number

The 2×4 brick started carrying it’s part number (3001) as of 1990 (Source: The Sphinx). Was that the year of introduction of part numbers in general? Did other parts start carrying their number before 1990, and if so, as of when?


  • From round to square-ish inside of the inner tubes.
  • Year inscription
  • (c) inscription