Their purpose is to keep tree limbs / branches from hitting your windshield by deflecting them above the roof line, thereby, avoiding damage to the windshield, A pillar and A pillar mounted lights. Also useful in jeeps without doors and windows whereby a whiplash of a branch from the windscreen can hit your face.
Limb risers are a fairly simple mod to fabricate and can be attached in front either to the body or the brush bar and at the other end to the top of the windscreen frame or a roof rack.
In some countries it is illegal to drive on the road with these since they can lethally injure someone in case of an accident and they must be removed when on the road.
Earlier explorers and road builders used to use razor wire for bush cables which would cut these branches rather than deflect them.
6mm diameter rubberized Steel Rope, Stainless Steel adjusting Rod
Suitable for Jeep Wrangler JK 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017.
1 Kit Branch Deflectors