I see it in MOCs all the time, and I’ve seen studs connect on half pins in official sets, but what about full pins?

Stud on pin

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    Legal in what sense? Commented Jan 8, 2020 at 18:20
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    Here's a related question asking about the Technic pin to Travis brick connection used in at least one official set: bricks.stackexchange.com/questions/9702/…
    – jncraton
    Commented Jan 8, 2020 at 18:35
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    @PeterMortensen There are certain types of connections that Lego set designers are not allowed to make in sets. Either because it stresses the elements or because it becomes to difficult to take the elements appart for a child. These techniques are colloquially called "illegal" Some lego fans choose to adhere to the same rules in their own creations, some do not. Commented Jan 8, 2020 at 19:21

2 Answers 2


The presentation that senior Lego designer Jamie Berard held at Brickcon 2006 and that spawned the entire legal vs illegal discussion can be found here:


The particular case you ask for is discussed in slides 9 and 10:

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    Very informative. Are there other official guides like this?
    – MrEvers
    Commented Jan 8, 2020 at 14:55
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    There are less such documents than you might think. Lego is rather secretive about there design processes. Jamie Berard has commented that he has come to regret disseminating this document and that internally they use an updated document that isn't available in the wild. Commented Jan 8, 2020 at 15:15
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    Why the regret, and why wouldn't Lego want people to know what connections add unwanted stress on bricks?
    – jamesdlin
    Commented Jan 8, 2020 at 22:19
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    Perhaps "regret" was a too strong choice of words. He implied something like that jokingly during a presentation I saw. The document itself generated a lot of discussion over the years. People started to take it very seriously, meticulously going over any lego instructions to search for instances where Lego might have broken there own rules (there are many to be found). Also, many lego builders didn't took too kindly to techniques in their creations being called "illegal". Commented Jan 9, 2020 at 9:28
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    I believe the lego group is hesitant to put out any official document on this because: - the aforementioned discussion it prevokes. - they being tied down by their own "rules". - as new connections are being invented all the time it is very hard to have a comprehensive document listing all things illegal/legal - possibility of leaking trade secrets which clone brands will take advantage off.. Commented Jan 9, 2020 at 9:56

According to LEGO, this type of connection is illegal, since the pin is stressed when connected to an anti-stud and eventually deforms.

People's MOCs do not follow same policy as TLG does. So you may encounter illegal connections from time to time. Pins are also cheap and usually owned in high numbers, so nobody's really bothered if one gets deformed.

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