International LEGO® Day 2025: moulding knowledge quiz

28 January marks the "birthday" of the LEGO® brick — the anniversary of the day in 1958 when the patent of the LEGO System 2x4 brick was submitted to the trademark office in Denmark. This is celebrated today as International LEGO Day.

As a way to celebrate as only New Elementary can, we decided to test your LEGO moulding knowledgeby posing a series of questions on our social media asking you to identify items in an image. Here are the questions and also the answers, so let's see how many you have right.

We asked if our readers knew what all the items in the image above were.  They all relate to the injection moulding process that makes new LEGO elements.

Question 1: Do you know what these two items are?

These are two examples of LEGO sprue, gates and runner complexes that form when the LEGO element is being injection moulded within a mould. They are a waste product of the injection moulding process, and the plastic is recycled as part of the LEGO moulding process. 

Generally, most people just call the whole thing a 'sprue' for ease, but this simplified breakdown shows the sprue, gate and runner sections. 

The sprue above is particularly interesting. There is a moulding machine in LEGOLAND® California that used to produce two 2x4 bricks and a sprue, in red acrylonitrile butadiene styrene (ABS, a type of plastic LEGO commonly use to create some of their elements). Normally, the machine would make the two bricks and sprue, eject them, shred them and then recycle it all back into the molten plastic. This sprue comes from that mould, having somehow escaped the shredder.

©2025 LEGO Group

Here you can see the 2x4 bricks within the mould with the sprue complexes still in position.

Advanced question: do you have any idea which elements might have been created on the ends of these sprues?

Question 2:  What is the thing in this picture? 

This is known colloquially as a LEGO cigar. It is not an element, but another waste product of injection moulding. LEGO cigars are plugs of ABS that form in the injection nozzle where the liquid plastic flows into the mould. At the end of a period of moulding, these plugs are ejected and normally recycled back into the moulding process.

There are lot of different LEGO colours represented here, and some can even even be marbled if they are ejected during a colour change.

Question 3: What type of moulding error does this minifigure helmet have?  

This red minifigure helmet demonstrates a moulding error. The molten plastic flows into the mould, but not enough plastic enters, and results in a defect known as a short shot.  

Short shots are a reasonably common moulding error, and most do not make it out of the factory as they are recycled. There are lots of people who like to collect such erroneous elements, as a particularly niche part of the LEGO element collecting hobby.

Advanced question:Can you tell what these elements were meant to be? Some are trickier than others.

Question 4: Do you know what the red things in the picture are?

This is ABS. Specifically, the pellets that are added to moulding machines where they are melted before being injected.  ABS arrives in its raw, milky white state before adding dyes to match the colour to LEGO’s wide ranging palette.

For a few years from 1969, LEGO also used ABS pellets to form the foliage on some elements. The brown element, like naked branches, would have green ABS granules applied to create a bush or tree.  These particular elements were short-lived as the granules could be prised off, or simply fall off, a hazard for a children's toy.  They looked great though!

Question 5: What is the significance of the name printed on this red 2x4 brick?

The 2x4 LEGO brick with 'Billund Moulding' print was given as a souvenir from the moulding factory in Billund following a tour of the facility. Billund was the starting point for LEGO, both in terms of its early origins as a wooden workshop and its plastic bricks.

©2025 LEGO Group

Since the late 1940s, plastic moulding of LEGO products has taken place in various factories around Billund. The very first plastic injection moulding machine arrived in 1947 and was placed in a barrack building adjoining the woodworking factory there. 

©2022 LEGO Group

While that original factory has since been replaced by larger facilities around the world, there are still moulding factories in Billund to this day.  You can read more about the moulding factories in Billund on the LEGO.com historical timeline.

67 years ago, today – on 28 January, 1958 – LEGO owner Godtfred Kirk Christiansen applied for a patent for a building system in which two or several interlocking plastic building elements “could be put together in a great number of mutually different positions”. This adaptation of Hilary Page's Self-Locking Building Bricks, including the critical addition of the underside tubes, formed the birth of the LEGO brick as we know it today.

Happy International LEGO day!

 

READ MORE: Review: 71497 Cooper's Tiger Mech & Zero's Hot Rod Car from LEGO® DREAMZzz™

Help New Elementary keep publishing articles like this. Become a Patron!

A huge thank you to all our patrons for your support, especially our 'Vibrant Coral' tier: London AFOLs, Antonio Serra, Beyond the Brick, Huw Millington, Dave Schefcik, David and Breda Fennell, Gerald Lasser, Baixo LMmodels, Sue Ann Barber and Trevor Clark, Markus Rollbühler, Elspeth De Montes, Megan Lum, Andy Price, Chuck Hagenbuch, Jf, Wayne R. Tyler, Daniel Church, Lukas Kurth (StoneWars), Timo Luehnen, Chris Wight, Jonathan Breidert, Brick Owl and our newest top-tier patron, BrickCats! You folks are just the cutest little baby bows.

All text and images are ©2025 New Elementary unless otherwise attributed.