What is a Leadholder?
Leadholder is a horrible name. It sounds like something that contains lead.
Artist’s Pencil with Movable Lead (Gurley Manual, 1874)
Leadholder (or Lead Holder) can be broadly defined as any durable instrument that is designed to hold and be refillable with consumable pieces of graphite so that the graphite can be conveniently used for drawing or writing. Within this definition there are subsets such as porte-crayons, mechanical pencils, and drafting leadholders. This website is primarily concerned with drafting leadholders, which are commonly called by draftsmen in the US as simply leadholders.
Because leadholders of this type are the specialized tools of draftsmen and artists, they are generally unknown to those outside this coterie. You can probably find one or two models at your local art supply store if you look hard enough. Not long ago you would have been confronted with dozens of makes and styles of these instruments.
This style of pencil has been referred to by many names including leadholder, lead holder, clutch pencil, refill drawing pencil, refillable pencil, artists' pencil, tubular pencil, drop pencil, and on and on. The mechanics of these pencils are, in general, not unique, examples of their various lead holding mechanisms (e.g. pushbutton spring clutch, twist lock clutch, and, occasionally, auto-advancing mechanisms) can be found in the common writing types of mechanical or propelling pencils. However, unlike most collectable pencils, leadholders are “working pencils,” that is, they are not designed as decorative objects or as a medium for advertising. Their aesthetics are really more akin to the workaday yellow wooden pencil, replete with foil stamped markings on the barrel.
Another attribute common among them is the diameter of their lead. The most common lead diameter being 2 mm. Other sizes available are 3.15 mm and 5.6 mm. These larger sized leads are generally soft and are used for sketching rather than drafting.
Use of the 2 mm leadholders, it should be noted, has been in decline amongst the also declining ranks of manual draftsmen (with the possible exception of architects) for decades in favor of pencils with smaller diameters of lead that do not require pointing. These smaller diameter (0.3 mm, 0.5 mm, 0.7 mm, and 0.9 mm) pencils invariably have an auto-advancing clutch mechanism akin to the common mechanical pencil.
The history of thick lead leadholders, I think, is nearly closed. In the 1950s there were hundreds of varieties, many of superior quality and with unique features. Now there are few manufacturers still producing them, and even fewer, I'm sure, with any desire to improve them.
see also: History of Leadholders and Leadholder Anatomy and Mechanics