I got this lockblocks to serve two purposes
On handlebars perpenduicular and if on helmut parralel

Since I no longer drive a car due to permanent eye problems, my bike gets me everywhere day or night. Night riding means you've got to have a light to be seen as well as to see where you're going. This flashlight holder is the best and most inexpensive answer I have found in the last ten years. The velcro straps are high quality and really grip both the handlebars and the flashlight. The rubber block keeps the whole thing aimed where you want it and I've never had one fall off. Easy to adjust, put on and take off with no tools needed. This brings up a small tip. If you stop somewhere to go into a store, don't just take the flashlight with you. Remove the holder too so it's not stolen like one of mine was.
Tip # 2. These holders strap onto many other round objects. You can have a light to illuminate your work area at night aimed however you need it.
I also own the larger one, the TWOFISH Cycleblocks Bicycle Flashlight Holder. You wouldn't be sorry if you bought one of each.

This is the most inexpensive wau I've found to get a headlight on my bike. ANd it is completely adjustable. Best money I've spent for my safety and visibility.

?? not yet

I have these on both of my bikes and now on my wife's bike. Work great with all smaller diameter lights.