USBDLM 4.50 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. The program lies within System Utilities, more precisely File Managers. This tool was originally designed by Uwe Sieber.
The most popular versions of the program are 4.6, 4.5 and 4.2. This PC software works fine with 32-bit versions of Windows 7. We recommend checking the downloaded files with any free antivirus. The current installer available for download occupies 1.2 MB on disk.
From the developer:
USBDLM is a Windows service that gives control over Window's drive letter assignment for USB drives. Running as service makes it independent of the logged on user's privileges, so there is no need to give the users the privilege to change drive letters. It automatically solves conflicts between USB drives and network or subst drives of the currently logged on user. Furthermore you can define new default letters for USB drives and much more.
You may want to check out more software, such as USB drive letter manager, which might be similar to USBDLM.