I searched the interwebz for Scarlet Spider props for a friends [http://www.instagram.com/superxluigi] cosplay outfit. I couldn't find any practical STL files for the belt and wristbands, so I decided to create them myself in Tinkercad.
The capsules have a 2 inch slit for a belt or wristband. You can either glue them down in place or only glue the 3D printed parts together and they can move freely.
The belt front is just a flat piece, not a belt buckle. You can attach it to the front of your belt.
Capsule: 3.5 inches x .75 inches
Belt base: 3.5 inches x 4.3 inches