Windows 7+ Taskbar Thumbnail Tweaker is a freeware from door2windows which lets you easily change the taskbar thumbnails' size, margin, spacing, max thumbnails and text height.
Apps from door2windows are truly free and DON'T include any offers to install 3rd-party apps/adware/toolbars/unwanted software and never will. The apps are portable and don't require installation.
Download door2windows App Bundledoor2windows App Bundle gives you access to all the latest apps released by door2windows in one download (along with future updates).
How to use:
Run the tool and customize the settings as you like. After you are done, click Change. The Windows Explorer will now restart automatically and you will be able to see the new settings which you chose. If you want to revert to the original settings click Restore.