When you buy the full kit it includes with a black washer to allow the receiver plate to fit 1/4. Is that also included in this or can I buy that individually as well?
Does this piece come with the hardware that will allow the plate to attach to 1/4 thread?
I'm not sure I understand your question. This item appears to include the receiver plate only.
When you buy the full kit (burgundy wedge receiver plate and the gray component that attaches to the camera) there is a black washer that allows you to attach the receiver plate to a 1/4 inch mount. without the washer it fits only 3/8 inch