Abstract: Structures for securing a fluid containment cylinder at the neck portion of the cylinder include a mounting frame having a bore disposed therein and a slot disposed orthogonally to the central axis of the bore. The neck of the cylinder passes through the bore and a u-bolt passes through the slot, registering against a shoulder on the neck of the cylinder, thereby securing the cylinder within the block. In other embodiments, the securing structure includes a collar for preventing rotation of the cylinder or for accommodating a certain degree of misalignment of the cylinder with respect to the securement structure.