Triple layer, durable flex bellow with interlock inner layer. Overall length 102 mm - 4in. Largest outer diameter 76 mm - 3in. 51 mm OD tube will slide into the bellow for 20 mm length, which makes welding to the end sleeves easy. Material stainless steel, weld sleeve material ferrite stainless steel. Can be used with both stainless and mild steel tubing.