1/2 inch (12 mm). How it all comes together. Universal Fit: Arrow T50; Stanley Stapler; Dewalt Stapler; Bostitch Stapler. Roofing felt, housewrap, insulation, weather-stripping, wire mesh, carpeting, canvas, roofing paper, vapor barrier, etc. Universal fit with Dewalt, Bostitch, Stanley, Surebonder and other brands that use T50 (1/2 Inch, 12mm) Staples. www.arrowfastener.com. Universal fit with Dewalt, Bostitch, Stanley, Surebonder and other brands that use T50 (1/2 Inch, 12mm) Staples. Designed and assembled in USA.