Update: I figured it out.
The QuickBooks_Estimate screen is based on the Estimate table yet One the EstimateLine grid is based on the EstimateLine table. If I add a new grid to a copy of the QuickBooks_Estimate screen I have the option to attach a table to the grid. The dropdown allows me to select the Estimate, DocumentLibraryLink and EstimateLine tables. I would like to attach a table other than these three options. How did the EstimateList table get into this dropdown if the screen is based on the Estimate table? How would I add additional tables to the dropdown list?
Thanks.