I am modeling a 5-1/2 buttress pipe thread form. 1 deg 47 min taper heliex. I am not sure on what plane the circle driving the pitch diameter for the heliex sould be on. On the flat end of the pipe? At the intersection of E7 and L7 from the chart ? or a plane .200 pitch of the end of the pipe? I have seen all three. I have attached a model and a chart.

Can anyone please help ?

Thanks

Bill