The OP/TECH USA FILTER CAP 58mm is designed to fit behind the filter and allows the stacking of filters without having to remove the cap. The additional filters will not cause vignetting. It also provides impact protection to the rim of the filter and lens which is often a common problem amongst avid photographers.
Protects the lens and filter from dust, moisture or impact
Held in place by the filter
Additional filters can be added without having to remove the cap