Bloc Loc Rulers work with any method for making half-square triangles (HST), so whether you prefer using paper or sewing triangles together, Bloc Loc is there to help you square-up perfectly each and every time. There’s no ruler rock or slipping either. Our patent pending channel technology locks onto your seam allowance which makes squaring-up so much easier and safer because you won’t need to put hand pressure on the ruler to make it work. Simply align the channel over the seam and trim. Bloc Loc rulers are easy to use, safer, allow you to square up in less than half the time and they make squaring up so much more fun!