usually defaults to the newest build, users often turn to tools that pull from official Microsoft servers [5.5, 5.15].
Official channels generally push users toward the most recent version, but there are ways to access specific builds: Media Creation Tool (Official) Microsoft Windows 10 Download Page provides the Media Creation Tool windows 10 1607 iso file download
Open Rufus and click the arrow next to "Select," then change it to Windows 10 Version 1607 ISO File Download Steps