To calculate the diameter of rivets that will suit your needs:
List down the thicknesses of the materials you need to combine. Say you need to combine a 5-mm acrylic sheet with a 2-mm aluminum angle bar.
Note the thickness of the thickest material. Since the acrylic sheet is thicker than the aluminum angle bar's thickness, we use 5 mm.
Multiply that largest thickness by 3 to find the minimum diameter of the rivet you can use. 5 mm × 3 =15 mm.
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