HD is only a collector designation. They were never officially called HD (or heavy duty). In England they were simply advertised as Rocket, in France they were "Gillette 500" because of the 500 francs price.It has only been since building my collection up, and been able to use different razors, that I have been able to appreciate and love the HD rockets. The name suggests some thing crude and aggressive - but they are not in the slightest.