Variations of structure:
A) machined type needle roller bearing
Na49, na59, na69, nki, nkis, bri, tafi, nao, na...2rs, etc.
B) machined type needle roller bearing without inner ring
Rna49, rna59, rna69, nk, nks, taf, rnao, rna, hj, br, ncs, mr, etc.