centering step 62 for a corresponding recess in the filter cap 8 to slide over the centering step and assist in centering and retaining the filter to the cage the cage 26 can be constructed with energy absorbing structural ribbing for example the cage includes one or more longitudinally angled ribs 80 that are formed at a non zero angle a shown in fig7 to the longitudinal axis 18 the one or more longitudinally angled ribs 80 can form a u201c barber pole u201d arrangement around the perimeter ofthe cage with a relatively constant rate of twist the ribs 80 form a support for the cage such as being coupled with an end of the cage to which the cage is coupled to the mounting assembly an impact or other stress load applied to the cage 26 such as in the longitudinally direction can be at least partially absorbed by the longitudinally angled ribs 80 through a bending deflection corresponding to a stress strain relationship and modulus of elasticity of the material used for the ribs 80 and connected structure essentially the longitudinally angled ribs 80 can function with a u201c spring u201d action from the impact or other stress loads one or more circumferential ribs 82 can be coupled to the longitudinally angled ribs 80 the circumferential ribs are disposed at some angle to the longitudinally angled ribs and spacing to each other as is appropriate for the particular size and.