A screw adapter to adapt a male thread. Equipped with 3/8" thread on the outside and 1/4" thread on the inside. Can be tightened or loosened with a screwdriver if required.
The Caruba 1/4-3/8 screw adapter has a screwdriver notch at the top, so it can be used over a male 1/4".
For example on a tripod plate, to go from 1/4" to 3/8".