TLR2947 has Tungsten Carbide balls
TLR2957 is not specified, so (probably) steel balls
Steel balls for a ball diff thrust bearing will not last you long, tungsten carbide will last you longer. Caged thrust bearings, like the ones from Avid RC. They have them with Tungsten Carbide like TLR, or even harder Silicon Nitride/Ceramic balls (
link) which I usually choose. In my experience diffs stay smooth for so much longer with a good thrust bearing
