coaxial or parallel axial members

δ1 = δ2  δ1 + constant = δ2  δ1 = δ2 + constant

 

axial members connected end-to-end in series

δ1 + δ2 = 0  δ1 + δ2 = constant

 

axial members connected to a rotating rigid element

δ1 δ2 ----   =   ---- a b δ1 -δ2 ----   =   ---- a b δ1 + gap δ2 ----------   =   ---- a b