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LEGO Techniques - Headlight Conflict

Finally getting back on track with the study on headlight bricks. A while ago I showed how headlight bricks are an odd construction. They maintain normal brick tolerance on 3 sides, but the fourth side actually reverses this and cancels out the tolerance on the opposite side. The effect is that of creating a true 2 plate high piece. But how does this affect SNOT construction?

Using my little tablescrap I've created two cases where the headlight brick creates error. The first is in the lower right corner under the yellow technic brick. You can see that the headlight brick is actually pushing against the sideways grey travis brick such that it doesn't want to rest easy. What's the deal?

First, a quiz: How wide is the yellow technic brick?

If you said 16.0mm, you're wrong. While it is that size nominally, the actual size is 15.8mm. Remember the 0.1mm tolerance on each side?

Using math, it's easy to see how the conflict can occur. The headlight brick is EXACTLY 6.4mm wide due to it's intended cohesion with a double high plate. The travis brick is exactly 9.6mm high. Added up, the total becomes 16.0mm which is obviously a little too much for our poor technic brick. You can certainly build up around such cases and get the bricks to be compliant but they will be stressed a little.

The second case is on the left where the headlight bricks interact with a blue and grey headlight brick. Using the same concept it should be easy to see what is happening. The red headlight brick atop the blue travis brick is in system... except for the stud face which is 0.2mm beyond. The width of the headlight/grey travis brick combo is again a true 16.0mm. The stuck out face of the headlight brick is pushing the grey travis brick (along with any connections) an extra 0.2mm further east. Therefore, even though the upside down headlight brick is attached to the blue travis brick, it's connection with the grey travis brick keeps it from pushing up against the brick.

Headlight brick, you are a wily one.


  1. Very interesting. Sheo has made similar observations and created an interesting diagram - have you seen it?

    Tolerance polarization:

    Failed connection 1:

    Failed connection 2:

    1. I have seen Sheo's. I had been working on this post off and on ever since REC4 ended oh so long ago. There's nothing highly revolutionary here, just a little easier on my head than Sheo's amazing studies.