Parker 1.0 mm lead pencil converter

By the 1930s, lead sizes for American mechanical pencils had been thoroughly standardized. There was the older standard of 0.046 inches (metricized as 1.1 or 1.2 mm) and the newer standard of 0.036 inches  (0.9 mm), and for drafting pencils there was 0.075 inches (2 mm). The plethora of odd sizes used in the 19th century had all been dropped in the first decades of the 20th.

So it was to my complete astonishment that I recently discovered that Parker, in the later 1960s, briefly adopted a completely nonstandard lead diameter of 0.040 inches (1.01 mm). Not in a mechanical pencil, strictly speaking, but for its "pencil cartridge", shaped like a Jotter ballpoint refill and used to convert any Jotter-style ballpoint into an injector pencil. The example shown above came in a sterling silver Classic ballpoint; it was still full of lead, but I thought I'd add a little more before offering it for sale (Parker didn't advertise these cartridges as refillable, but all it takes is to hold one tip-up, press the back button down, and feed new lead into the front). Yet when I put in some 0.9 mm lead, it didn't work properly. The lead was held firmly when the end button was released, but when the button was depressed, the lead shot out instead of advancing a millimeter or two at a time. Upon closer examination, the original lead that came inside the cartridge measured a hair over 1 mm and worked perfectly -- as did some 1.0 mm lead that I then added as a test.

According to Jotter: History of an Icon, p. 204, Parker's pencil cartridge was introduced in 1968 (other authorities specify that it was at the beginning of that year). No mention is made of the lead size used, however, though in external form our 1 mm cartridge is the earliest model shown, all metal with only a bit of black plastic at the end, and no eraser. How long it remained in production is not clear, though I was able to find the image below from a 1969 Parker catalog, originally posted by Graham Hogg here.

It seems clear that Parker adopted a slightly oversize lead diameter to prevent users refilling their cartridges instead of buying new ones. Customers would assume that the cartridges were worn out, never suspecting that the lead diameter was the issue. Indeed, Parker advertised the cartridges as being good for up to a year, or up to 50,000 words -- clearly positioning them as consumables, despite building them stoutly enough for years of service.

I haven't had the time to go back through all the different Parker pencil cartridges in my shop to check lead diameters, but I've handled quite a few of them over the years and this is the first I've found that didn't work when refilled with standard-sized lead. My guess is that later models all used standard lead, and that perhaps even the original model was reconfigured at some point to use standard lead as well.

ADDENDUM: At the Columbus pen show I was able to ask around about this. I found only one person -- a former Parker employee -- who knew about the 1 mm lead. Unfortunately, this was from observation, not company lore, so we still don't know how this all came to be. Did Parker anticipate that consumers would try to refill the cartridges, and made them to use the nonstandard lead from the beginning? Or were they originally made to use standard lead, and a modified version using nonstandard lead was introduced only later, after the problem of refilling became apparent?