Y level or Wye-level consists Y-shaped frames which supports the telescope. Telescope can be removed from the y-shaped supports by releasing clamp screws provided. These y-shaped frames are arranged to vertical spindle which helps to cause the rotation of telescope.
Compared to dumpy level, adjustments can be rapidly tested in y-level. But, there may be a chance to frictional wear of open parts of level.
In case of Cushing’s level, the telescope is restricted against rotation in its longitudinal axis and it is non-removable. But, the object and eye piece end can be interchangeable and reversible.