This post plug is made of brass and fits the large detachable brace post assembly   

Nickel Silver Threaded Post for Large Detachable Brace Post Assembly without the Radius  

This nut is made of nickel silver and has a straight knurl.  the thread is 1/2 x 32 and it is a component of the large detachable brace post assembly   

Nickel Silver 5/16 x 32 Knurled Nut is part of the small detachable brace post assembly

Nickel Silver Radius 5/16 x 32 Threaded Post is part of the small detachable brace post assembly