I’m sure you will be surprised to hear that a guy like me just couldn’t let something like that go by! An investigation would have to be launched.
Out with my micrometer! Mine is a 0-25mm, in 0.01mm increments – that’s about 0–1 inch in 0.0004 inch increments. The small piece of original unknown brand lead in my Waterman measured 0.715/0.72mm diameter. The two Staedtler leads that kept falling through measured 0.685/0.69mm and the one that worked measured about 0.695mm. Well, that seemed to support my theory that the problem was related to the lead diameter.
So, just what size are 0.7mm leads? 0.7mm plus or minus how much? Obviously Staedtler think 0.685 – 0.695mm is OK, but Waterman don’t because that size doesn’t work in their pencil. I grabbed a few 0.7mm samples from other brands and got to work with my micrometer. I’ve rounded the results to 0.005mm bands as there is a bit of variation in each piece of lead, and from one piece to another of the same brand.
Mitsubishi Uni = 0.685 – 0.69mm
Staedtler = 0.685 – 0.695mm
Pilot Eno = 0.70 – 0.71mm
Waterman = 0.705 - 0.71mm
Faber-Castell = 0.71 – 0.715mm
Pentel = 0.715 – 0.72mm
The original piece in my Waterman = 0.715 – 0.72mm
In all my years of penciling, I don’t think this has ever happened to me before.