2 * STROKES: The best filter in the world can*t do its job if there are leaks in the seal of the airbox. That*s why Twin Air provides a complete line of products to ensure a leak-proof, fool proof fit. Twin Air*s PowerFlow kit comes with a rigid, lightweight, billet aluminum cage that provides a tight seal to the airbox and replaces your flimsy plastic stock cage. 4 * STROKES: Twin Air PowerFlow kit for 4-Stroke models: Replace your air-restricting stock backfire screen with our New PowerFlow kit. The kit includes a rigid, lightweight, billet aluminum cage with a special backfire-resistant layer of foam laminated to the inside of the filter.