Windows NT 4.0 Service Pack 6a (SP6a) resolves the SP6 issue with Lotus Notes and other Winsock based applications and provides the latest updates to Microsoft Windows NT Workstation 4.0 and Windows NT Server 4.0 (including Enterprise Edition). Windows NT 4.0 SP6a contains known Year 2000 updates for Windows NT 4.0. This version provides 128-bit encryption capabilities for computers running on the Intel (x86) platform. The High Encryption version of Windows NT 4.0 SP6a is eligible for export from the U.S. to all customers worldwide, except to U.S. embargoed destinations.
If you are unsure whether your NT 4.0 system needs this service pack, refer to Microsoft's documentation.
Here's other similar drivers that are different versions or releases for different operating systems: