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that would be a size P crochet hook
it is best to use an H or I size hook
A 5.0mm would be an H-8 hook.
In UK sizes, a 2mm crochet hook is a 14, it doesn't not have a US size equivalent. Here is a chart with crochet hook conversions from metric to US to UK.
A 0.9 mm steel hook is about a US size 13.
A size 5 steel hook. http://www.crochetmagazine.com/hook_sizes.php
A 3mm crochet hook is halfway between a C and D size in US sizes.
For yarn, use an "E" or an "F".
It's not totally clear here what you are asking. If you are asking if you can get a 50mm (approximately 2 inches) crochet hook, I think you could--but what are you making that would need a broomstick-sized hook? Are you looking to find a "size 59 metric crochet hook"? It wouldn't be easy, the largest hook I've seen has been a size 'Q' which is 15mm. If you want one bigger, you would have to build it yourself, would be my guess.
00 is a steel hook size. Manufacturers vary in their mm sizing. I found 00 hooks listed as 2.75 to 3.5mm If you have a particular hook and you need to know the mm sizing of it, I suggest you purchase a Crochet Hook Size Gauge Tool. The knitting needle ones do not give accurate sizing for a crochet hook. Annie's Attic sells these and I'm sure other stores do as well.
A size "C" crochet is generally around 2.75 mm in the United States. There isn't really any specific standards regarding crochet hook sizes, different manufacturers made their hooks in different sizes, and that pretty much still is happening today.
In the US, knitting needle sizes are in numbers; crochet hooks use both numbers and letters.