F17 is a stress grade for Australian hardwood under AS 2878, used where higher strength or longer spans are needed than MGP10 softwood. This page is an indicative, educational guide to F17 rafters, ceiling joists and beams at 450 mm and 600 mm spacing, common species (Spotted Gum, Blackbutt, Sydney Blue Gum) and how F17 compares with MGP10. It does not reproduce the copyright AS 1684 span tables — read every allowable span from the published tables.