VW splitwindow buses have a lot of sharp angles. At the beginning of the 60’s VW started designing things to make sharp (and) dangerous edges safer. This protection cap for your mirror arm is a very good example for that… yes this was original in 1961 as far as I know, and I understand even less why they only used it for one year… The modern purist would think that  this is a better way better for airflow, and he’s right! But ithe especially esthetics is the most important today, it’s a little different and it's especially cool looking! A small neat detail to your beloved one.