Check the listing for details. S1D 2.5" x 4" Flex Couplers to Isolate Vibration & Stop Cracks 8520-2 2-Pack. Color: Silver, Condition: New. Listed at 41.99 USD. The Squirrelly 2.5 inch x 4 inch Flex Pipe Exhaust Couplers are engineered to provide exceptional performance and durability for your vehicle's exhaust system. Designed to effectively isolate engine vibrations from your exhaust components, these stainless exhaust pipe liner couplers significantly reduce the risk of cracks in downpipes, cat-backs, headers, and turbo manifolds, ensuring smoother and more reliable performance. The flex coupler features bellows with an interlocking lining that enhances exhaust flow through the coupler, preventing excessive back pressure and outperforming standard stainless steel pipe flex couplers that often create obstructions or turbulence in the exhaust track. This design ensures optimal engine performance, making these couplers an ideal choice for any.