Hi David, if your box or rectangle is axis-aligned then it can be quicker to use the "Edit size" menu. You can access that by clicking on the size field in the properties panel, here:





If your box is not axis aligned but has a line edge that runs along the entire length you want to set you can select that edge. Then the size control will have a Length: value showing and when you click on that you'll be able to edit it.

If you want it to stretch only in that direction like Scale1D then uncheck the "Maintain proportions" option.

- Michael