hanging multiple picture frames of different sizes in line and with equal spacing
Forget the sawtooths. Buy some picture wire and small screws. I like short #6 panheads for most pictures. Maybe #8 for large pictures.
Attach the screws about 1/3 from the top on each side. Drill pilot holes so you don't split the wood. Don't screw them all the way in, leave room to wrap the wire.
Attach the picture wire so the hook will be inside the frame recess. Wrap around each screw and twist the wire on itself.
Buy or make a picture hanging tool. To make one, start with a stick about a foot long. Put a hook on one end and a cabinet knob on the other end. You can substitute many things for the knob, you just need something that will allow you to hold the stick while the picture is attached. The hook will be down and the knob will be up. Measure up 8 inches from the hook and put a mark.
https://www.amazon.com/Picture-Hanging-Level-Hanger-Yellow/dp/B083J75P7F
https://www.bobvila.com/articles/picture-hanging-tips/ (see tip number 4)
Hang the picture on the tool and position it on the wall. Put a small mark on the wall at the mark on the stick.
Measure 8 inches down from the mark on the wall and nail in the hook to the wall.