This is a customizable version of a RAM® dual-ball-and-socket mount. There are other similar designs available here, but I could find none that met all of these criteria at the same time:

• fully customizable
• accommodates different size balls on each end
• structurally stiff
• can be tightened with fingers, needing no tools

The STL file provided here is an example only. You must customize this for your own needs. The photograph shows my GPS adapter plate with a 20 mm ball on the left side and my wife's car phone 17 mm ball mount on the right side.

Customizing

The ram_mount.scad script requires the included octosphere.scad script (originally from my geodesic sphere library) to be included in the same folder or in your usual OpenSCAD library folder.

Set the parameters however you want. Keep the arm length as short as feasible to prevent them from flexing too much when you assemble the mount and tighten the bolt.

Press F5 to preview if the preview does not update.

When you preview the model, OpenSCAD displays the minimum bolt length required in the console output. Be sure you obtain a hex-head bolt at least this length, with a compatible hex nut. For most purposes an M6 bolt is sufficient.

When you are satisfied, press F6 to render (this may take a few minutes), and then export the model to an STL file.