To understand the chronological succession of brick types, logotypical and other inscriptions, and technical improvements introduced in the basic LEGO construction elements, they have to be considered in their whole.

As a company, LEGO made periodical investments in molds. New molds might be required because the old ones were worn out, because it was necessary to increase the output, or because of some former technical limitation that had to be overcome. The full-bodied studs, for instance, were incompatible with shorter injection cycles, because the mold opened too soon and the stud surface, still soft, would cave-in. Thus, hollow studs became a must once new, faster injection equipment became available in the mid 1950s. Even before that, mold numbering started being used, so as to readily identify dirty or otherwise impaired molding units.

This text proposes a new approach to the study of the early evolution of the LEGO bricks, in which each cycle of new mold acquisitions will be considered in its characteristics that are common to all cases, and particularly the geometry of the brick studs, the logo and the inscribed mold numbers. In this manner we shall be able to identify contemporary molds of different brick types. When one of these types is dated, all molds with identical distinguishing characteristics will, in all likelihood, be contemporary. Have fun!

Studs are very slightly conical. Height 2,0 mm. Seen in profile, the edge at the top of the stud is rounded.

The studs are full (not hollow). When the mold is opened too soon, the stud top caves in, resulting in a slightly concave surface. The shorter the molding cycle, the more concave the surface.

The bricks themselves are not marked with the LEGO logo. No mold number.

Slotted but only two types exist: single slot or two opposed slots.

Bricks known: 2X4 and 2X2 in white, red, several shades of yellow, green, and blue, transparent (creamish and greyish), and marbleized over a brown basis. See examples HERE.

Studs are very slightly conical. Height 2,0 mm. Seen in profile, the edge at the top of the stud is only very slightly rounded (almost sharp).

The studs are full (not hollow) and because of that, when the mold is opened too soon, the top caves in, resulting in a slightly concave surface. The shorter the molding cycle, the more concave the surface.

The bricks are marked with "LEGO" in large protruding letters.

Inside each brick there is a protruding line, parallel to an edge.

No engraved mold number. During the timespan of the molds, a number was manually scratched onto, at least, the 2X4 molds (the white brick above is not numbered, the blue has a "4" faintly visible on the right side).

Bricks known: 2X4 and 2X3 in white, red, yellow, blue, green and transparent. Colors are homogeneous (no relevant shades).

NOTE: The early bricks were unmarked, as were the set boxes. The reason may be related to the fact that the system was strongly inspired by the English Kiddicraft. G. Istok in his "Unofficial LEGO sets/parts collectors guide" indicates 1952/53 as the year of the first boxes branded "LEGO" and this must coincide with the branding of the bricks. This is also coherent with the fact that the first 1X2 bricks share a mold of the same type (see below).

Studs as above but height 2.2 mm in the 2X3 bricks.

The bricks are marked with "LEGO" in small protruding letters. "G" of "LEGO" almost closed.

As before, inside each brick there is a protruding line, parallel to an edge.

No engraved mold number. All 2X2 and 2X3 bricks seen had a mold number manually scratched onto the mold (the 2X2 bricks above are nrs 4 and 3, while the 2X3 is nr 2).

Bricks known: 1X2, 2X2 and 2X3 in several colors.

Studs as above but height 1.9 mm. Bricks have depressed circles machined underneath.

The bricks are marked with "LEGO" in small non-protuding letters. "G" of "LEGO" open. No protruding line inside.

Bricks have a mechanically engraved mold number, in slightly protruding type.

Bricks known: 2X3, 2X8 and 2X10 in several colors.

NOTE: At least the 2X3 brick from these molds is known unslotted.

Studs cylindrical with rounded top edge. Height 2.0 mm. Studs are not hollow but seen from the top they sometimes show a slightly protruding edge (seen on the top right stud in the white brick above) or protruding center (same, lower left).

The bricks are marked "LEGO" with the so-called "dog-bone logo" (see the red 2X4 above), except the 1X2 bricks that are unmarked and the 1X6 and 1X8 bricks that use the logo minus the crossing horizontal bar.

All bricks have a mechanically engraved mold number, in protruding type.

Bricks known: 1X2, 2X2, 2X3, 2X4, 2X12 and 2X14 in several colors. 1X6 and 1X8 in white. 4X4 corner.

Studs cylindrical, top edge sharp. Stud body full (not hollow). Underneath (usually under each stud) there are circular areas that slightly protrude from the surface.

Bricks marked with a neatly protruding mold number (except 1X1).

"LEGO" marked on the top of each stud. Stud top often concave because the plastic in the thick stud is not cold enough at the end of the injection cycle.

Bricks known: 1X1 (square and round) and 1X2 (white and red); 1X2 and 1X4 round (white, red, and clear)..

In the 1X2 brick, logo lengthwise.

Bricks known: 1X1 (square and round); 1X2 (square and round), 1X6, 1X8 (white, red, clear, blue, yellow); 2X2, 2X3, 2X4 (white, red, clear); 2X8, 2X10 (white, red).

Studs cylindrical and marked with the LEGO logo. Stud body hollow, as above. The hollow is a plain 3 mm opening in the underside, often with irregular peripheric edge.

Bricks with underside tubes to engage the studs of underlying bricks.

Under the bricks is inscribed the text "Pat. / pend." When the text is in the correct position to the reader, the mold number will be on the right side and turned to the interior.

Bricks known: 2X2, 2X3, 2X4, 2X 8, 2X10 (white, red, clear, blue, yellow). Possibly new 1X2 mold also manufactured at this time.

NOTE: in some rare instances (e.g. 2X2 nr 10) the mold number is on the left side and turned to the interior. I'm not aware at this moment whether these bricks were molded in Denmark.

Studs cylindrical and marked with the LEGO logo. Stud body hollow, as above. The hollow has a shaped entry (a peripheral annulus, often faint). Diameter of the hollow smaller than above: circa 2.2 mm.

2X bricks with underside tubes to engage the studs of underlying bricks, as above. 1X2 bricks with the "LEGO" logo sideways.

Under the 2X bricks is inscribed the text "Pat. / pend.". Molds identified by a number. When the text is in the correct position to the reader, the mold number may be on any side, but usually is on the left side in 2X4 bricks.

Bricks known: 1X1, 1X2, 1X2 round, 2X2, 2X3, 2X4.

NOTE: a few rare transitional 1X2 bricks have a lengthwise logo but a circa 2.2mm stud hollow.

As above but the shaped hollow entry annulus is better defined and more regular, sometimes protruding. The mold reference is the combination of a number and a letter. On 2X bricks the reference will be seen as a number on one of the sides of the brick, and a letter on the opposite side.

Lisbon, Portugal, first uploaded November 10, 2008