An apparatus in an example implementation includes a vessel that includes an inner wall and an outer wall. The outer wall includes a first set of grooves configured on an interior portion of a bottom of the outer wall. The inner wall includes a second set of grooves configured on an exterior of the inner wall. The first set of grooves are configured to interface with the second set of grooves to secure the inner wall and the outer wall together. In more specific embodiments, the first set of grooves and the second set of grooves are provided as ascending steps such that a rotational force applied to one of the walls operates to engage subsequent steps in each of the first and second sets of grooves. The walls are configured such that a rotational force creates a force being applied to the lip to secure the walls together.