B triangles as radii, points 6, 7, 8, and 9 are established in the same manner as were points 2, 3, 4, and 5.
With point 9 as a center and a radius equal to the hypotenuse of triangle 9 to F, an arc is drawn bearing away from point B. This is intersected by an arc drawn from point B with a radius equal to line BF of Fig. 280. This establishes point F.
A curved line is now drawn through points 1 to 9. Straight lines are drawn connecting points F, B, and A. If both sides of the pattern have been worked simultaneously, the whole pattern has been developed and locks may now be added as shown.
The straight lines representing the square base are treated according to the type of joint adopted for the system of piping, of which this "fitting" is a part.
