Hi,
I'd like to buy a box of 12 Mitsubishi Hi-uni pencils from JetPens but I don't know what lead hardness to pick.

I use pencils for writing and sketching, I like a dark line on the sheet but I don't want to sharpen the pencil too often.

At the moment I'm very happy with the Mars Lumograph B.

What Mitsubishi Hi-uni hardness could correspond to the Mars Lumograph B?

Thanks,
Carla

Lead hardness is universal. Grade B from one company is the same as from another. So, the answer to your question is: Grade B.

Hi, my experience is a bit different... As an example Castell 9000 pencils have a harder lead comparing to Mars Lumograph. I'd say that a Mars Lumograph B corresponds to a Castell 9000 3B.

That's odd and should not be that way. Check out this article on Wikipedia.

In practice, I have also found that there are difference in darkness and performance among brands regarding graphite degrees:
http://robotninjamonsters.blogspot.com/2007/06/graphite-party.html

While I have not tried a Staedtler Lumograph wooden pencil in a while, I bet that you would probably be quite happy with a dozen of HB to start with. If you prefer not to have to sharpen often, you could even go with a dozen of F pencils that would give you the same darkness of an HB with the hardness of an H pencil which make it ideal for drawing fine lines and writing.

Hi-Uni pencils are yet another thing I've been delighted to find on JetPens. I found some loose Hi-Uni HB's in a brick and mortar store, so I was able to try them. They are beautiful pencils, probably the best I've ever used. But for me HB is too soft--I write with them, but don't draw at all. Since I use my pencils for writing, I'm concerned with keeping a sharp point and keeping smearing to a minimum. When I order a box I'll probably get the "F" (that's what I usually use in mechanical pencils). I expect if I were an artist I'd want a softer pencil, or more likely I'd want an assortment.

Actually the Mitsubishi Uni-ball F leadholder is one of my favorite sketching tools. The F lead keeps its sharp point without sharpening for long periods of time and can still lay down a nice dark line with heavier drawing pressure. Qualities that also make it a clean and effective writing clutch pencil.

Any idea on when the HB grade is expected to be restocked?

No idea, but you could simply click on the notifications button to be alerted automatically when the HB grade is re-stocked. If in a hurry, the F grade might just do the trick having the same darkness with a slightly stronger lead which retains its sharp point longer between sharpenings.