Why is a marijuana cigarette called a joint?

The reference below gives this:

joint (n.)

c.1290, “a part of a body where two bones meet and move in contact with one another,” from O.Fr. joint, from L. junctus, pp. of jungere “join” (see jugular). Slang meaning of “place, building, establishment” (esp. one where persons meet for shady activities) first recorded 1877, Amer.Eng., from an earlier Anglo-Irish sense (1821), perhaps on the notion of a side-room, one “joined” to a main room. The original U.S. sense was especially of “an opium-smoking den.” Meaning “marijuana cigarette” (1938) is perhaps from notion of something often smoked in common, but there are other possibilities; earlier joint in drug slang meant “hypodermic outfit” (1935). Meaning “prison” is from 1953.

The most pertinent part is probably the path from when it had been used, in America, as slang for ‘”an opium-smoking den”‘ with my guess being that, since marijuana was easy to obtain compared to opium (hence the dens, with the drug and the equipment of choice), people seldom actually went to anything remotely like an opium den (“joint”) but rather had their own private “joint” any time they toked up with one or more other people, hence the word transitioning from meaning a physical place to meaning the virtual place created when one toked up and eventually therefrom to being the item itself.

But that’s my guess, based on the material on the site. Notice the folks there made a different guess about its further evolution though they did not cite the year of the later uses as it changed.

And of course, it has changed otherwise as well: we no longer even remember it having any hint of an opium den, but usually think of a joint (outside of the marijuana usage!) as being a, perhaps seedy, liquor establishment on the insulting side of the word or as a pleasant, sort of cool sounding, self-chosen description for one’s establishment. And somewhat separately, as in “let’s blow this joint.”

The term “Joint” was given to a marijuana cigarette by 50’s and 60’s pot smokers as the cigarette resembled an electrical joint in shape. In the late 50’s to early 60’s, new electrical insulations came out that enabled electricians to tape the insulation on with rubber tapes, and the shape of the splice looked similar to the Marijuana cigarette, hence, the nickname of the Marijuana cigarette became a “joint”, as the electrical connection was named.
Tapes used to cover higher voltage splices to prevent arc protection that was made out of asbestos surely made these “electrical joints” look almost exactly the same as the marijuana cigarette, so, the name stuck to the cigarette for years to come.

Not many people know the true meaning, because this was named after a low voltage “telephone” wire splice, as these splices actually resembled the “joint”, and the telephone splices had an uncanny resemblance.

The source of this name has not actually been proven to be taken from the electrical joint, or the telephone wire joint, but, I have been told over the years by many techs that this was the reason why this name stuck to the joint.

I’d like to post a picture of the joints I am talking about, which are still made till this day.. In this picture, the electrical joints are circled , which we think today are still the original thing which the marijuana joint was named after. These “splices” that join medium voltage power cables together still are called joints, and very much resemble the marijuana joints shape and color if they are covered in the white arc proofing tape as shown in this picture.

These “joints” are stacked together as three, so, it is hard to see what I am saying, but, when one stands alone, it looks exactly alike, and I have been told by some of the Vietnam Vets that worked in the trade that this is what the “joint” was named after, where the name originally took place in NYC. Somebody please let me know if this is accurate, I have been trying to verify the authenticity to this claim, as well, maybe find if it originated from this or the telephone splice.

JOINT – (1952) a marijuana cigarette [from the ‘joining’ of the drug with the tobacco to make the cigarette;]

Also: http://www.straightdope.com/classics/a1_290.html

I think it is because when they want to make a marijuana cigarette , they empty the normal cigaret and fill it with marijuana. and sometime they put the marijuana in the special paper similar to normal cigaret paper and they roll it and smoke it like cigars in past times.