The Cisco UCS-C Series servers come with a terrific tool-less slide rail kit. The rail kit is compatible with 3/8" square hole and 1/4" round hole racks. The rail kit does not work with 2post racks and threaded hole racks.
I found two adapter kits from The Server Rack.
The Threaded Hole Rack Adapter Kit
The 2Post Rack Adapter Kit
That is all...