Thank you for clarifying. The pads are integrated with the posts, which is why I asked. The way you described it could imply smooth or threaded posts and you didn't post a photo. Go look at how pads are fitted on a AD990 for an example.

the pad length does not matter!

Are you doing tricks where you might be moving forwards or backwards? If so, a pad with a really long trailing end designed for mountain bikes might provide inconsistent braking. There are freestyle specific pads that might work better. Look at the difference between the photo posted above and something like Odyssey Slim By Four pads for example. The rubber compound is usually indicated by the color and some pads work better than others depending on the rim's braking surface finish.