Hi Shaolin,

Not, there is currently no way to adjust the width of the separator. It's hard-coded to 1 pixel wide. You should Submit a Feature Request and perhaps this can be added to the grid in a future release.

In theory, you could increase the size of the UIElement using a CreationFilter, but this might have unintended consequences, because the elements on either side of the separator would not move - thus the separator would overlap the cells (or vice versa) and I suspect this would results in some weird painting problems when you moved the mouse over the cells nears the separator.

A better alternative might be to use a DrawFilter to draw a thicker separator. Once again, this would cover part of the cells, but in this case, you could control when the drawing occurs and make sure it paints over the cells. I'm not absolutely sure this will work - there might still be some painting issues due to the grid invalidating the cells or the separator. But if you want to explore that option and you don't mind covering up part of the cell, let me know and I can help you with a sample DrawFilter.