Leatt 5.5 FlexLock Boot - WhiteULTIMATE COMFORT AND FORCE REDUCTION PROTECTION. The Leatt 5. 5 FlexLock boot, was a 3 year project with long term development and testing using our Pro athletes from all over the world! The 5. 5 boot is a real head turner when it comes to looks and style, but the design brief was comfort and protection also, and we nailed it first time. Leatt's adjustable FlexLock system reduces forces to the ankle by up to 37% and the knee by up to 35% by Locking