Any little peice of wood will work for a reducer. I keep strips of 3/4 x 3/4 board from 2in to 12in long around my hives all the time if I see I need to reduce an entrance for whatever reason I put a peice in of what I think may be the right length. If they get crowded looking at the entrance and no robbers around take it out and put in a shorter one. But I always keep the opening on the same side.