Steve is spot on. The T-Rig will leave around 1/2" head in the tube for a Texas Rig, the Tube jig will leave aprox 1/4" so you can insert the jig in the head. The inserts are changeable so you can choose one or the other and always change your mind later.
There is also a blank that can be inserted in the spline if you want your tube solid.
Jason