StudioG's Custom weapons are 3D-printed resin weapons designed for your model kits. They come in parts so you can paint them more easily. They have pegs designed into them for fitting. However, they do not snap-fit together. Super glue is needed.
It's recommended that you sand them with 400, 600, and 1000 grit sandpaper to prepare the surface for painting. Once painted, you can glue all the parts together and apply water decals and such.