The screens hold the packing material to the outer wall of the muffler and make putting the baffle in much easier.Steve also said that it gives more internal volume to the muffler which helps power.I would just go one wrap with a little overlap to hold it.I only used the wrap from one muffler to do both and threw the rest away with the stock baffles.From his website: 2012-2014 CVO Perforated Muffler Sleeves
The new Fullsac muffler sleeves are highly recomended when installing our CVO Power cores. Starting in 2012, Harley began over stuffing the OEM mufflers with an excessive amount of sound absorbing material. Dyno testing has shown a loss in TQ when muffler volume is reduced. The new perf sleeves allow half of the packing to be removed while holding the stock material to the outer wall. This creates the needed air gap between the inner core and the outer wall in the muffler. A dyno proven combination that produces great sound quality and performance.
Retail Price $ 59.00 pair