Joining multiple stl parts into whole model

[OG56]

Lets say I have stl model that was already separated into multiple parts.I.e. the model designed to be 3d printed separately part by part and then to be put and glued together manually.
For my own reasons I would prefer to print the model as whole part rather then separately. The problem is when I import multiple stl files into blender then are not connected inside a Blender(See attached screenshot).I tried to put all parts together inside Blender by dragging them inside each other but it is close to impossible task.
So my question is there any quick and dirty way to somehow automatically joint all parts within Blender or any other application ?


Thank you.

In blender:
Enable Addon: Object: Bool Tool

Bool Tool > Auto Boolean > Union