Antenna mast half.stl is for mounting a 3/4" pvc pipe to a 1 1/4" antenna mast, for mounting homemade antennas for example.

Antenna mast to mast half.stl is a coupler for mounting 2x, 1 1/4" antenna masts to each other.

Both files have holes for #8 bolts to secure them together. 2 prints are needed to make a complete coupler.

You'll need to print a minimum of 2 and most likely 4. I'd suggest using washers under both the head and nut of the bolt to help distribute the clamping pressure as tightening it down can cause it to delaminate.