This is a replacment rubber guard for the Vertex Standard VX-231, VX-351 and VX-354. The rubber PTT guard goes in behind the plastic ribbed push to talk cover.
The rubber PTT guard protects the ptt button itself preventing water and grit ingress and is an integral part to the protection and operation of the Push to Talk assembly.
The other required item in some cases is the Plastic PTT Cover.
This can be found here Vertex Standard Replacement PTT Plastic Cover