For some reason, most reasonably priced propelling pencils only seem to be available in 0.5mm, which may make a nice fine line but will break with the slightest pressure causing you to go through leads at an astonishing rate.
These good quality German made propelling pencils may cost a few pennies more, but they take 0.7mm leads, which while still precise are substantially more durable - even if you are scribbling something down in a hurry.
Ergonomically designed and comfortable to write they have a nice sturdy clip and a rubber under the cap.
