This is, according to the Fisher Body Service Manual, the floor mounted
rear armrest for certain A-body hardtop cars from 1970 to 1972. These
are similiar to what you see on the convertible models, except they are
for hardtops. I know the 70-72 Olds Cutlass Supreme uses these.
I have a LH and RH in black and a LH and RH in blue. And another
LH in blue. They are all in good shape and would work fine for a
driver.