[From the question: Why do I have leftover parts? What is this orange thing and where does it go?]
LEGO are aware that people lose small LEGO bricks all the time. That’s why they give you extras of things like 1×1 plates and 1×1 tiles. Some sets use a lot of different colours of these types of bricks and you may end up with quite a few spare parts. This is normal.
If you have extra pieces that are more like regular bricks or larger parts, then there is a chance that you may have made an error in the construction of your set. It’s not unheard of but it is really unusual for a set to contain a spare 1×6 brick (for example). Go back and have another look at the instructions. If there is a parts list at the back of the instruction booklet, see how many of that piece you are meant to have. If it is a spare, then congratulations! It doesn’t happen very often.
The exception to this rule is with the 3 in 1 Creator sets where you may have leftover bricks from building any of the models as those bricks may only be used in one of the other alternate builds.
Some sets contain a Brick Separator. These are not meant to be part of a model and are designed as tools to help you separate LEGO bricks. They are meant to stop you using your teeth or fingernails. The picture shows the most recent design. These come in green or orange. The older version comes in dark grey or green.
.
the plastic brick house 
I Always thought the extra parts are there because of the way they sets are packed.
From each brick needs to be the exact weight of these blocks there before they go in the bag. For the smaller bricks there could be one brick more because of the the weight difference. Say 5 small bricks way 4,6 grams the system will want 5 grams in there so it ads another brick.
Anyway, great site.
LikeLike
I’ve seen the LEGO packing process in person. The weighing process of each bag’s contents is very accurate. The parts are sorted into reusable boxes and weighed before being packed in film. Every so often, a box is pulled out and manually checked against an inventory. Barring very rare errors, each extra part is there deliberately.
However, the reason for the duplicate parts is not just that smaller parts get lost easier, but because as the number of parts in each bag increases, the quoted maximum tolerance of the weighing machine gets closer to the individual weight of a small part. So rather than risk a very rare missing part, any parts which are close enough to that tolerance are duplicated. Some parts used to be duplicated but are no longer routinely done (e.g. cheese slopes) which suggests that the weighing process may have become even more accurate over the years, but, unlike the rest of this post, this is my supposition.
LikeLike
So, if I edit to mention the tolerance of the packing/weighing then that would be okay?
LikeLike