I use a 3rd arm, I got mine through campbell cameras but you can find them else where cheaper. I don't think I will own another camera arm. Its well made and movement is very smooth. Depending on what type of camera you are attaching to it would depict the model you need to get.
I'll have to look at mine sitting, collecting dust. "Muddy. . ." something or other, I forget. Good quality arm that can take a fluid style head and a decent sized camera yet priced so it didn't take me for a ride like Campbell's tries to dole out.