The screws in the bottom holding on the visor tend to interfere with the fit at the lower edge of the mount. I wondered why they were so small (4-40 IIRC), and I discovered that anything bigger keep the unit from fully seating, and it won't snap in properly. I ended up notching the mount in 2 places where the visor screws & nuts poke out, so the nuts wouldn't prevent it from fully seating. HTH YMMV