If E is a real Banach space
then ℬ(E) is the space of all bounded linear operators on E, and 𝒵(E) the subspace
of M-bounded operators, i.e. the centraliser of E. Two Banach spaces E and F are
considered as well as the tensor product E ⊗λF. There is a natural mapping of the
algebraic tensor product 𝒵(E) ⊙𝒵(F) into 𝒵(E ⊗λF). It is shown that
𝒵(E ⊗λF) is precisely the strong operator closure, in ℬ(E ⊗λF), of its
image.