Nora,

Going by millimeter measurement, a 7mm hook would be above a K. Perhaps an
L? I don't have one on hand, so can't check for you. I know they make
them, though they're hard to find. N's, P's, and Q's are easier to locate.

By the numbering system we use here in the states, it would fall exactly
between a G and an H.

Knitting needles in size 7 (UKor US standard) would be 4.5mm in diameter,
which would equate to a size G hook diameter.

Another possibility is that the pattern was designed before the major
manufacturers really standardized the measurements. I have an old Gem hook
that's listed as size I/9, but it's 6mm in diameter. Every hook I see now
that happens to be 6mm in diameter is a J/10. If this is the case, then the
pattern may actually call for an H.

Size 7 steel hooks (no letter) are made, but I'm certain they're too small
for anything except crochet cotton thread. It's the steel hook size we
tended to run out of most often at Hobby Lobby, and it's also the one I use
most often, unless I'm crocheting with sewing thread (13/14 steel one for
that).

I guess the best thing to do would be see if the stitches in any examples
are fairly tightly placed together, or loose and "floppy". If it's floppy,
go with a hook around the L or so. If not, just keep trying from G and on
up until you find a hook that matches your gauge. Personally, I'd start
with the H, as it seems to be what my gut tells me is most likely.

Anastasia

---not that you'd really need to be told all that last bit, but I added it
because who knows who might check the archives for this later on?