This is an AWESOME Vintage Metal FOLDING RULER by Reliable Stamping Company somewhere between 1913-1922.  After that it became the Rustless Rule Co in Buffalo NY. Patents numbers are: 1069186, 1501712, and 1501713.

It can open up to 48" nicely 

It is steel and I believe bronze at the joints.  Check out my other items. Payment within 3 days of winning. Pay Pal only. Thanks.