Watch band sizes

The smaller band will connect to the larger Apple Watch, but the plastic insert will not reach the edges of the Apple Watch case, and leave semi-circle edges that can catch on things and even scratch your wrist.

If you are trying to use an existing band, then give it a try.

If you are buying a new band, then get the correct band for the Apple Watch.

No. You would need a band made for 42/44/45mm Apple Watches.

I wouldn't need to. Apple Watch bands sized 38/40/41mm are NOT designed for Apple Watches sized 42/44/45mm. Plain and simple.