By tubular metal spacer, I am assuming that you mean the Solid thru-shaft and not the aluminium reducers. With the metal thru-shaft you use a vise and line it up straight with the eyelet and press it in. Once it is in...off center the shock in the vise and press it the rest of the way through. Becareful not to press the vise on the rebound knob or and part that might break. It should not take much pressure.