If it is indeed a screw type back it will have indentions ON the back (6 to 8). A special tool is required to remove the back without damage to the watch back. Any reputable jewelry store should be able to remove the back. If there are no indentions then it should be a pop back. Some watches do not have a slot to slide a pry tool under the back. You have to use a sharp knife..taking appropriate safety precautions.