A simple project box. Internal size is 40mm x 60mm x 16mm but it can easily be customized by coping the project in OnShape.com and adjusting the dimensions.

The lid is screwed together with M3 Allen Bolt Socket Cap (like this http://goo.gl/Jnydhb). Different length will work depending on the box depth. I find 8mm - 10mm to be sufficient in most cases.

Here is link to the public OnShape doc
https://cad.onshape.com/documents/d093c5d8f90c4948aeade364/w/cd33db4a28a14506b50a4969/e/ea4f0b380e2d42328c9253ee