The following items are what I would suggest you order - and order these per mounting post.
Order the Rockwood SP1003-630 1/4 - 20 x 2 1/4" 1" Diameter Decorative Thru Bolt - Satin Stainless Steel as seen here:
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Order the Rockwood SP1079 1/4 - 20 Double Cone Head Union as seen here:
Order two each of the Rockwood SP1026 1/4 - 20 x 5/16" Set Screws (Standard) as seen here: