Not a "trac" bar, but a "traction" bar. Believe it or not, they're different. Your YJ comes equipped with a "trac" bar front and rear. It's used to keep the axle lined up laterally underneath your Jeep. It is mounted parallel with the axle.
The "traction" bar is a carry over from drag racing. Generally (and in my case) it is a bar that is mounted perpendicular to the axle and runs from the top of the axle forward to some location on the frame or crossmember. Here's a pic or two of mine (there's one on each side):
Mine was custom. Sam's Offroad also sells a one size fits all kind of ladder bar. There have been some reports that these ladder bars are binding during articulation though. Here's a pic of Sam's: