While creating a web browser app I was a little surprised that there is no easy way to set a ToolStripItem to spring or stretch as you can in a StatusStripEx. After trying a bunch of stuff and getting close myself I opened a ticket and got some great help (Special thanks to Vallarasu S.) and I thought it my help others to post the answer here. I have included a sample app that demonstrates it both in SDI and MDI form.
Sizing turned out to be tricky because you cannot use the position of adjacent controls to help you. In the tool strip the items do not have Top, Left, Bottom, Right or location properties. all you have are the sizes. So I figured find the size of the whole strip and add everything up. Add the padding, margins etc. And sub tracked that from the size of the strip and and you have your new width. Now where to put it? Hmmm.... Well it turns out the right place is to override the Layout event and put it in there. All is demonstrated and commented in the code example. Hope this helps someone.
Shannon McCoy
ToolStripExLayout_2edb50d9.zip