French 8x50R "TS 39 R I" Lebel

What is “R” in this headstamp?

I believe it stands for Rugles, the company supplying the metal.

R, H, Y are all from the company called : Societe des trefileries et laminoirs du havre
R is from the Rugles factory
H is from the Gravilles factory
Y is from the Pont de Cheroy factory