Direction of fit

Okay, imagine you have a hat and a head. You can put the hat on your head or take it off. The hat is said to have a "direction of fit" that is "from without to within". This means the hat is made to fit onto your head from the outside, and that is the way it should be worn. You can't wear your head on the hat!

Now, let's imagine you have a key and a lock. You can put the key into the lock or take it out. The key is said to have a "direction of fit" that is "from within to without". This means the key is made to fit into the lock from the inside, and that is the way it should be used. You can't put the lock into the key!

So, things can have different directions of fit depending on how they are designed to be used. Hats fit on your head, keys fit in locks, and so on. Understanding the direction of fit is important because using things the wrong way can cause damage or not work at all.