I've been using these for years. They are indispensable for fly tying. My vision started to go in my late forties, but with these I have no problem tying even the tiniest flies.

Just like the listing. Magnifying lens is held on with hex nuts so you can change to a different magnification if you buy other lenses.
The headband has an adjustment knob at the back that takes it from small to large. I included some photos of this as a loose guide for your sizing

Have NO idea why this TOOL is being called a 'toy' ...
It is a magnifying optical visor i.e. 'Optivisor' and Donegan's is the very best on the market. Nothing else comes close. You may wish to review the product more fully and realize that the LX is the 'lightweight' version which in essence means that the lens' are plastic. The Optivisor is also available with glass lens'. Since plastic will scratch more easily, consider that. On the other hand, save some money on the LX and just be as careful as you always should be with a professional grade tool. I recommend the two and a half lens for starters. You can always buy more or less powerful lens as you need them. They interchange. You don't need another base visor. Also look up the optional 'loupe'. It attaches easily and is very helpful in extreme closeup work. I used to use mine often polishing out molds to 8 micron by hand.

GOTO: [...]

This headband magnifier has an adjustable headband. The lens is very clear.

I have been doing a fair bit of small detail work on the scroll saw, and I have been facing three issues. I get close to the blade so I can see the detail (too close for my bi-focal prescription) and can blow off excessive sawdust. When this happens, I end up straining my eyes and half closing one to help focus/relieve the strain. Alternatively, I stay further back to my prescription focal length, but I find that I frequently lean forward again before I realize it and then the eye strain starts again.

Finally, I recently tried using a free standing lighted magnifying lens, but it only had one lens. If I did not have my head held just so one or both eyes would be distorted from the edge of the lens. Also, using the lens, I had a much harder time telling depth perception and timing for various cuts. Needless to say, I did not use if for long.

Then my eye doctor gave me one of these to try have purchased a product sample. I immediately knew that this product was the answer for which I was looking. There are two independent, identical lenses and it mounts on the head. I am able to use both eyes for binocular vision (a big plus), it doesn't matter how I twist my head, it is only the distance that determines the focus independent of the angle of viewing. The image is nicely enlarged and I don't have to strain my eyes to see the details like I have been.

The visor that raises and lowers isn't anything special, but it does the job. I haven't had any problem with the mounting, but I have not been very hard on my set. I can understand how others are having problems as the mounting pieces are by no means high quality parts, but they do the job and have worked for me thus far.

The strap barely fits my head, but I know I have a big head (and no, that's not just because I think a lot of myself) and have always been uncomfortable in all but the largest of hats and helmets. If I had a complaint, it would be that the strap does not hold vary tight, without the nob allowing the headband to loosen. I have not docked a star because I have had no other troubles with it and it does keep it just tight enough that the visor isn't sliding around. I can also raise and lower the visor itself without the head band slipping. Even so, I still think it feels loose.

Overall, I am really happy with my purchase. I can now work longer at fine detail work without the usual eye strain. I would recommend this item for anyone who spends any length of time at fine detailed work. If it is just a quick something, this item might be helpful, but in that case you may be better off with a simple magnifying glass (its cheaper).