For many years now we've used 1/4" crown, 1 1/2" or 1 3/8" staples for frames. They hold even without glue if you use 2 staples at each end. However, the best I have ever used is a 3/8" stapler with 1 1/2" long staples, which is exactly the right width to straddle the groove in the bottom bar and you only need one staple at each end. Senco is the only manufacturer that currently has a 3/8" gun and they are fairly expensive at $350.00, but well worth it when you have thousands of frames to build. We use a 1/2" stapler with 1 1/2 " or 1 3/4" galvanized staples for our boxes. The large staples come with an adhesive/resin coating. Forget taking the box apart once stapled, as you will destroy the box!