In a flat throw, the club rotates parallel to the body plane rather than perpendicular to it. There are two common types of flat throw known as 'inside' and 'outside' flats.
Inside Flat Throws
The club is thrown and caught with the palms facing inward, towards your body. Usually just one spin is used, although it is possible to do more. The club's body goes up first, followed by the handle, and the throw travels straight across your body at about chest height:
Hold the club near the centre, at the top of the handle. Inside flats are almost impossible to do with your arms in their normal juggling positions because they take up so much room while they are in the air. Move your hands further apart so that your upper arms stick out from your body to the sides at about 45°. Making your throws a little higher than normal, to give yourself more time, can often help in the early stages.
Outside Flat Throws
Here the club spins in the opposite direction to inside flats. Because of the shape of the throw, and the throwing action that is required, it is much easier to do them as over-the-top throws rather than as normal cascade throws (i.e. an outside flat should be thrown over, not under, the incoming club, as in a reverse cascade). Outside flats are usually thrown and caught with the palms facing forwards and hands raised up to about eye-level:
However some jugglers find it easier to let the club turn a little more and then make the catch with the palm facing inwards:
Notice the direction in which the club is pointing when it is caught, the body points inwards on the palm-out catch and outwards on the palm-in catch
I find the palm-out catch to be preferable, because the rotation of the club forces the weight into your hand as you catch. Catching with the palm facing in means that the rotation and weight of the club will pull the handle out of your grip, making it harder to grasp. Again, because the club rotates parallel to the body plane, you have to make the throws wider than normal, however because your forearms are pointing up rather than down as with inside flats, it is possible to tuck your upper arms in near to your body thereby making the pattern look tidier. Catch the clubs near to the top of the handle for a narrow pattern, and near to the end of the handle for a wide pattern.