Recommend me a keychain light to compliment my HDS...

[Hondo]

In particular, follow that second link to the original Sapphire, Don goes into all of the detail of the relationship to Peters Arc AAA there. In short, yes, heads should interchange.

 

[fyrstormer]

I contact Don on a regular basis.

I have in fact read the Sapphire 25 thread. Scroll down and you'll see I specifically referenced the Arc AAA Ti in a post I made back in 2010. As previously stated, even back then I knew the titanium Arc AAA was a clone of the Sapphire and is therefore interchangeable, but Don never directly stated in that thread whether the aluminum Arc AAA was interchangeable with the Sapphire.

I had forgotten about the original, non-regulated Sapphire. You're right, Don does mention in his description that the original Sapphire was designed in collaboration with Peter Gransee and has the same threading. That was a decade ago and I simply forgot.

 

[dorikinhajime]

I have been toying with the idea of my back up light to be a keychain cr123 flashlight. If my hds ever needs a battery I can pull it from the back up light.
I have narrowed it down to EagTac D25c MKII, I considered Olight Mini, E15 cr123 light off of Aliexpress, fourseven mini. I will update if you like.