These lovely geometric experiments were built by Huw Millington for our parts festival, The New Black, and I have saved them until last. When choosing parts to include in The New Black I didn’t only go by colour; I also strove to include many parts from the family that contain connection points based on the 3.18mm diameter such as bars, and the clips and holes that grip them. Huw's models use the hinge joint created with parts 23443 and 11090 and then, to connect multiple triangles together, he used another part selected for The New Black; the Technic axle connector with two projecting holes that can receive a bar (Design ID 24122).
They are all useful, small LEGO elements that have no stud connections. Many people still imagine that the LEGO System only connects via the studs and the antistuds but of course the System has developed a long way beyond this over the course many decades. One of the 'connection families' (I just made that name up) I have examined in the past are the 5.9mm ball and cup connectors, first used in the Chima Legend Beasts and the Mixels, which were introduced to satisfy the need for poseable joints in smaller models.
So how - and why - did the '3.18 connection family' enter the LEGO System at all? To find out, I looked back through the history of LEGO parts. This article would not have been possible without the wonderful contributors to BrickLink.
PinsTo discover where this seemingly arbitrary measurement of 3.18mm came from, look inside a LEGO brick. Specifically the ones that are one stud deep like the 1x2, 1x3, 1x4 and so on. Following the granting of the LEGO brick patent in 1958, these bricks were given ‘pins’ to clutch the brick below, and these pins are fractionally less than the distance between two studs. (I'm not certain if these pins were always precisely 3.18mm in diameter, as LEGO clutch has been tweaked over the decades, but for simplicity's sake I will call these 3.18s.) Here's a pretty 1x2 brick (Design ID 3004) from 1976.
READ MORE: Why did LEGO redesign all the arched bricks?
As far as I can tell, the first elements with recessed studs that could fit a 3.18 are Technic bricks, which first appeared in 1977. This makes sense; the Technic System was quite a redesign of the brick and embraced new possibilities for building. Having recessed studs on a brick means you can place a wider brick on top that is offset by half a stud. My surviving-yet-beaten-up childhood box of 871 Supplementary Set proves this is both possible, and intended.
However this doesn't prove that this was the sole or primary reason why Technic bricks were given recessed studs. Once again I haven’t found any certain evidence and it is quite possible that it was for a technical reason with the finer aspects to the Technic brick's design or to allow for a smoother moulding process. Regardless of the reason, the genesis that led to the 3.18 connection family is perhaps here.
1978: Year of the 3.18BrickLink’s list of parts released in 1978 confirms this; many parts with recessed studs were introduced including the seminal 1x2 jumper plate (3794). I haven’t tested every 1978 part with recessed studs to see if they can take 3.18s, but those I have do. In most cases, fitting a modern-day 3.18 bar into a 1978 recessed stud is a slightly tight fit. However, as this picture shows, I also offset a 1x3 brick of 1978 onto the two recessed studs of a 2x2x3 75° slope brick (3684) of 1978, and it was a smooth fit. Finally I tried a modern-day 1x3 brick on the 1978 slope and again it was tight, perhaps suggesting the standard in 1978 was fractionally less than 3.18mm, both for the underside pins and the recesses in studs?
The importance of 1978 to the 3.18 connection family goes far, far beyond recessed studs, however. As I’m sure you recall, it was the year that the minifigure with moving arms and legs was introduced. I am certain no one could have predicted the varied and strange ways in which the minifigure would impact every aspect of the LEGO brand and its products, and the roll-on effects of their introduction into System. That said, LEGO designer Jens Nygaard Knudsen put an astonishing amount of thought into designing a characterful figure to exist within the rigid LEGO grid and the design of the hand in particular is extremely clever. Each measurement serves a purpose within System, for example the external diameter of the hand’s C-curve is (about) the same a stud, so it can connect to an antistud. The distance between the curve and the cuff of the arm is just enough to fit the underside lip of a brick. However it is the diameter of the hand’s internal curve that we are interested in here. It can hold - you guessed it - a 3.18, so a minifigure can grasp an underside pin.
I’ve reverse-engineered Jens Nygaard Knudsen’s thought process as he designed the minifigure hand - in other words, this is pure conjecture! I imagine making the exterior of the C-curve the size of a stud was a relatively obvious design choice, and he then needed a slightly narrower dimension for the internal curve. Being a good designer he sought out an existing dimension within the System that he could leverage to some use, and found that in the diameter of underside pins. Either that, or the concurrent development of the Technic brick led him directly to this solution.
Either way, it naturally followed that the basis of all minifigure accessories would be a 3.18 bar. It’s worth making clear that although I’ve been talking about "3.18s" for this whole article, up until 1978 there were no parts based on 3.18 bars (that I am aware of). For example, old LEGO signs had axle-like poles (that snapped all too easily) and the bars of other accessories such as the Homemaker Hand Mirror / Indian Paddle were not 3.18mm in diameter, or even round in many cases. The first 3.18 bars appeared in 1978 in the form of shields, swords, halberds, axes, pickaxes, paddles and, most beloved of all to me, shovels and brooms which came in my first-ever set with a minifigure, 605 Street Crew (above). That set also contained a System piece with 3.18s that wasn’t an accessory; the 1x2 plate with handlebars (3839). The rolling-out of parts with recessed or open studs that also occurred in 1978 is presumably in response to the development of the minifigure accessory, rather than the Technic brick.
Building a familyAlong with more accessories, 1979 saw the introduction of another 3.18 part that also connected with studs: the antenna (3957). In 1980, two important parts with open studs appeared: the 1x1 headlight 'Erling' brick (4070) and the 1x1 plate with clip light (4081, shown below in Grey and Bright Blue [TLG]/Light Gray and Blue [BL]. The wider ones are the redesign from 1983). Erlings and clip lights are more famous as SNOT parts that allow sideways building but this doesn't negate the fact that fixing a 3.18 sideways was also an exciting development.
4276) came and went and the bar/clip connection proved to be the logical way forward. Undoubtedly, this year's introduction of the hinge that Huw has used has further assured the LEGO Group's commitment to the 3.18 connection family.
READ MORE: Inspiring ideas for using LEGO bars and clips in your models, from our "New Black" parts festival
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