Adjective : an inflexible steel rod. ,an inflexible determination. ,inflexible rules.    From Dictionary.com. 

This accounts in a measure for his coolness, his self-possession, and that kind of uncompromising rectitude or inflexibleness that marks his career, and that he so lauds in his essays.    From Wordnik.com.  [Birds and Poets : with Other Papers] Reference

That this inflexibleness making me desperate, I resolved to add to my former fault, by giving directions that she should not either go or correspond out of the house, till I returned from M. Hall; well knowing, that if she were at full liberty, I must for ever lose her.    From Wordnik.com.  [Clarissa Harlowe; or the history of a young lady — Volume 7] Reference

Thou mayst perceive in these tears the steady, unalterable laws of heaven, the inflexibleness of the divine justice, that holds thee in adamantine bonds, and hath sealed thee up, if thou prove incurably obstinate and impenitent, unto perdition; so that even the Redeemer.    From Wordnik.com.  [The World's Great Sermons, Volume 02 Hooker to South] Reference

My sister’s taunting letter, and the inflexibleness of my dearer friends — But how do remoter-begun subjects tend to the point which lies nearest the heart! —.    From Wordnik.com.  [Clarissa Harlowe] Reference