You are looking at one brand new 10 pack package of 1/4" (6.4 mm) post antique nickel pinwheel Chicago Screws. This item 4862-21 has a threaded post that allows you to open and reattach pieces whenever needed. These screws work great for straps, cases etc.
Dimension:
When Closed 1/4" (6.4 mm)
Cap 1/2" (12.7 mm)
Base 7/16" (11 mm)