Deformable spacers and spacer assemblies absorb energy when flange bolts are subjected to compressive axial loads by plastically deforming, failing in shear, rupturing or in a combination of failure modes so the flange bolts and the flanges connected thereby are not damaged. One deformable spacer may have a hollow cylindrical body with a plurality of elongated slots there through. Another deformable spacer may have an annular stiffener extending inwardly from an inner surface of a hollow cylindrical body. A spacer assembly may include an inner cylindrical body, and outer cylindrical body, and an annular shoulder extending from one of the bodies and engaged by the other body shears when a shear failure load is applied to the flange bolt. Another spacer assembly may include an annular belt around a cylindrical body so that the belt will rupture before the cylindrical body plastically deforms.