What are the setting to allow uploads of .stl files

Here is how to change the allowed file upload field types:

https://www.jotform.com/help/29-How-to-Change-the-Allowed-File-Types-Extensions-in-the-Upload-Field

The file upload size limit can also be increased:

Here is our quick guide detailing how to increase the limit as well as the maximum file sizes for different integrations:

https://www.jotform.com/help/33-Changing-the-Upload-Size-Limit