I have read that the 30x and 60x  Jewelers loupe are what to have. I have a 10x , not strong enough. The 30x dia. is I think 21 mm. and the 60x is really small. I just found a 40X loupe with a LED light That is 1 inch (25mm) in dia. for $9.99 I will get it Monday. I think that will be great.