Graphics3D[{ CapForm[None], Tube[{{0, 0, -1}, {0, 0, 1}}, .2], CapForm["Round"], Tube[{{1, 0, -1}, {1, 0, 1}}, .2], CapForm["Butt"], Tube[{{2, 0, -1}, {2, 0, 1}}, .2], CapForm["Square"], Tube[{{3, 0, -1}, {3, 0, 1}}, .2] }, Boxed -> False]