1/4 inch (6 mm). How it all comes together. Universal Fit: Arrow T50; Stanley Stapler; Dewalt Stapler; Bostitch Stapler. Window screens & shades, shelf papers, closet linings, etc. Universal fit with Dewalt, Bostitch, Stanley, Surebonder and other brands that use T50 (1/4 Inch, 6mm) Staples. www.arrowfastener.com. Designed and assembled in USA.