A:You really can't thin or split dreads easily. How thick your dreads are depends on how much hair is in them and taking hair out of dreads is difficult. Cutting them down the middle with scissors or a knife is a really bad idea. Because of the way the hairs are packed cutting them will make the dreadlocks way shorter and thinner, pretty much ruining the dreads. I know, I did it to one of mine the first month I had them.
So if you can't cut them what do you do? It depends on how mature they are. If they are fairly new, less than 3 months, the easiest way is to back comb them out starting at the tip and working toward the root. After you comb them out you can redread them. You'll notice a lot of loose hair coming out of the dread as you backcomb it out. This is all the loose hair that would have naturally fallen out when you brushed your hair. You'll also notice it takes a long time to comb them out depending on how dreaded the hair is. Take your time and progress down the length of the dread slowly. Anytime you're removing dreads you'll find Dread-Zasta makes things a lot easier - the more developed the dreads are the more Zasta becomes indispensable.
What if the dreads are compltely mature? Well there are a few options and none of them are very good. The quickest and most popular way is to rip them all the way down starting at the root and ripping towards the tip. The drawbacks to ripping are that it hurts and it still shortens the dreads a lot because so much hair is lost in nearly all cases. Less hair is lost than with cutting but they will end up shorter and thinner than the rest of the dreads.
Usually ripping leaves you with one long dreadlock and a second smaller dreadlock. The larger dread with be much smaller at the root now but won't loose any length. As it grows it will be thinner at the root since some of it's hair is now in the short dread. After the longer dreadlock grows out a bit more you can clip it off where it gets thicker if it looks funny.
A variation on that last method would be to tie the dread at the base into two separate dreads. You could use hemp or whatever you like. As the dread grows out from the root continue to tie the new growth separating the dread into two separate dreads. Then after it has grown about a few inches you can rip the dreads apart where they are still joined. This method takes quite a while since you have to wait for the dreads to grow but what's the rush really? Especially since the dreads will look good throughout the entire process. Then, if worst comes to worse and you loose most of the original, un-split length when you rip, you'll still have the new growth, which will all be the right size.
For the most part if you don't need to split dreads or make them thinner you should try to avoid it. Usually people that have dreads with 1" sections or even a bit larger don't want to split them or make them thinner. A lot of people though that have dreads bigger than an inch and a half consider splitting them to have more dreadlocks and more fullness. If you do decide to split your dreadlocks try to keep a minimum section size of 1/2". Smaller than that any you'll likely have problems getting them to lock as they grow unless you have very textured/curly hair.