Polyurethane upgraded gaiter for all knuckle joints and many track rod ends. 
Please note, this does not fit all track rod ends as so many genuine and aftermarket parts have been supplied in 60 years. It does however fit every suspension knuckle ball joint ever made.

Current rubber gaiters seems to have short life span but these cured polyurethane rubber items exhibit physical properties that are generally tougher than silicones, so they are more resilent to wear and tear for this application.