Comments about Pentax Pentax O-LC77 77mm Front Lens Cap:

Be advised that picture is wrong, it applies to the old model while this is the new model - the one with Pentax in large silver font on the front (at least is what I received from Adorama). This is relevant as the old model was more reliable and had better grip ergonomics than the new one.
I had ordered this as a replacement for the otherwise identical 77mm cap that ships with DA* 12-24/4. The original cap fell apart when one stopper then the other one on the same side snapped away. Several months later the stopper breaks off on the replacement. I am not sure whether this is due to wear, having dropped the cap or both but I certainly don't abuse my gear.
Secondly, while the inner grip seems to have better ergonomics in fact it is more slippery than the outer grip of the old model.
It does look like this design is flawed on both reliability and usability. Having several lenses with 77mm filter ring I am now considering hunting online the old type cap for all of them.
Good luck finding yours.