A:AnswerHello there! The HQ8 has been replaced by the SH50. The HQ9 replacement heads are compatible with AquaTouch (AT9__) and PowerTouch (PT9__) shavers.
A:AnswerThey may change the design and hence the model number but the razor you own isn’t going to change so the replacement heads will be the same as when you bought it. I found several styles, including the replacement heads I needed, at Beat Buy.
A:AnswerProbably not a good idea.
Each model uses a specific set of blades and screens.
The shaver has the specific blade information printed on the outside or the inside of the blade compartment.