Bars are made in different sizes and materials which can effect compatibility. Typically, steel bars come in two sizes - standard and oversized. Standard / regular size bars have a 1-1/4" outer diameter. Oversize bars have a 1-3/8" outer diameter. Aluminum bars have an oversized 1-3/8" outer diameter, with the same inner diameter of a standard steel bar. Here is a quick look at the size and type of bar each compression system requires.
SCS - requires bars without a slit; some SCS only fit standard bars while others can fit any bar
HIC - bars need a slit; oversize steel bars only
IHC - bars need a slit; standard steel bars or oversize aluminum bars
ICS - bars need a slit; need a star nut inside the bar, oversize aluminum or standard steel bars
Pytel - bars need a slit; oversize aluminum bars only
Threaded - bars need a slit; oversize aluminum or standard steel bars