A supplemental type certificate (STC) is a type certificate (TC) issued when an applicant has received FAAapproval to modify an aeronautical product from its original design. The STC, which incorporates by reference the related TC, approves not only the modification but also how that modification affects the original design.
The AD Toolbox makes it easy to search through the approved STC holders. To do so, simply navigate to the STC category in the lefthand NavBar:
You can search by make/model, i.e., "UH-60":
Or even description, i.e., "anti-rotation":
