The Tamworth Letter Receiver shows the change made for two horizontal slots where the cap is wider to give protection to the mail. Several systems were tried to protect the vertical slots that are still shown in the mould. The Royal Australian Historical Society is offering a 20% discount on Adel Briggs' book 'Cast Iron - New South Wales Letter Receivers' for users of Flickr. Call the RAHS on (02) 9247 8001 or email admin@rahs.org.au to order your copy and mention Flickr to receive your discount!