Karl,
If you have a 1970-1985 Behr Evaporator Box....
This "screw & bushing" oddity attached to your evap blower motor assembly. Strange.
I'd guess someone added this because the motor was slipping in the round plastic housing. Occasionally when we work on clients cars of this era (1970-1985) we come across a round plastic housing that is cracked or broken, however most are quick fixed using a simple hose clamp. I'd say someone went a different avenue in trying to fix an issue where the evap motor was slipping through the round plastic housing.
The original factory design, to secure and hold the motor, inside the plastic motor support bracket, is simple: its a slip fit into the round plastic housing that is support by 4 plastic stanchions, and the motor is secured to that using 4 metal clips. There is a lip on the round plastic housing that "stops" the motor from moving all the way through; the round metal motor case sits against it.
3 images above compliments of MThomas58
Kuehl Hurricane Blower Motor Upgrade