A Stepping ring is a ring with a female filter thread on one side and a male thread on the other. The threads are different sizes so a filter can be attached to a lens with a different sized thread.
There are step up and step down rings and these are always from the lens to the filter. If you have a lens with a 52mm filter thread and a 49mm filter you would buy a 52mm to 49mm step down ring. If you have a lens 49mm filter thread and a 58mm filter you would buy a 49mm to 58mm step up ring.
Take care that you don’t obscure the edges of the frame when using a stepping ring. This is more common on step down rings where the edges protrude into the frame and cause vignetting. You may also find the increased depth of the ring causes vignetting on wide-angle lenses. Use the camera’s depth-of-field preview to see if any vignetting is occurring.
