Top tube adapter adds a top tube for carrying step-through, suspension, and other non-conventional bike framesDesigned for use with hitch and trunk mounted bicycle carriesFor Bicycles with a measurement of 18"-28" stem-to-seat postEasy installation - no assembly or tools requiredMAX WEIGHT: Maximum bicycles weight 45lbs. Not for use with E-Bikes. Our Retrospec Bike Rack Cross-Bar Top Tube Adjustable Adapter was engineered to give you the ability to mount bike frames with openings between 18”-28”, such as women's step-thru frames, full-suspension, and other unconventional designs. A built-in internal spring creates the tension needed to keep your bike safe and secure during travel. The durable plastic coated hooks ensure the paint on your bike frame is protected from any scuffs and scratches. Whatever your cycling destination maybe be, the Retrospec Bike Rack Cross-Bar Top Tube Adjustable Adapter will be sure your bike arrives safe and ready to ride!