I assume the one on the left is a later one? Can anyone help with approximate dates and what the extra plate is for (keeping water out perhaps?)etc?

email (option): ian@integsci.com

Hello Ian.The one on the left is the early one.Prewar BSA brake drums had a short tube riveted to the inside that fitted into the circular plate on the brake plate.Maybe it was to stop grease finding its way onto the brake linings.If you can find exploded drawings of prewar BSA hubs you will see what I mean.Sam.

email (option): smarwick@iprimus.com.au

Many thanks for the information Sam.

email (option): ian@integsci.com