What is the proper way to connect 10awg wire to connectors rated for 14awg wire?
The correct answer is to use approved wire twist on "wire nuts", or split bolt.  The package description will usually say how many and what sizes are allowed.

For example, the common red twist on "wire nut" will hold up to five #12s, officially.  There is a diagram and chart on the product which gives examples for mixing different wire sizes.