STL files are commonly used in 3D printing and computer-aided design (CAD) to represent 3D models. If you're working with STL files, you may want to quickly preview them in Explorer without opening a dedicated 3D modeling software. Fortunately, Windows Explorer makes it easy to view STL files without any additional plugins or applications. Here's how to do it:

1. Open Windows Explorer and navigate to the folder containing your STL file.

2. Once in the folder, you should see the STL file listed alongside other file types.

3. To preview the STL file, simply enable the 'Details' view in Explorer. This can be done by clicking on the 'View' tab in the Explorer menu and selecting 'Details' from the Layout section.

4. In 'Details' view, you'll see a thumbnail preview of the STL file, along with file properties such as size and date modified.

5. To get a larger preview of the STL file, you can enable the 'Preview pane' in Explorer. This can be done by clicking on the 'View' tab in the Explorer menu and selecting 'Preview pane' from the Panes section. The preview pane will display a larger image of the STL file along with some additional properties.

6. With these quick and easy steps, you can effortlessly view and preview STL files directly in Windows Explorer, allowing you to quickly assess 3D models and streamline your 3D printing workflow.