Flatback Elbows Components & Parts > Trust IAC for Pneumatic Industrial Equipment & Material Handling > Elbows > Flatback Elbows Flatback Elbows with Replaceable Back Flatback elbows feature a bolted - replaceable back plate made of 10ga. abrasion resistant steel. Mortar Filled Flatback Elbows Mortar Filled Flatback elbows use a standard bend and add a steel box across the back wear radius filled with a mortar material, generally cement. Flatback Elbows Flatback elbows feature a bolted – replaceable back plate made of 10 ga. abrasion resistant steel. The elbow body is constructed of 12 ga. steel.