Found a GC holed up in his trailer trying to figure out this one: (Wracking the brain and internet)

What are the triangle, or diamond markings every 19.2" or 19-3/32" for?

19.2" makes five joists every 8 feet. It's the intermediate density between 16" centers (six joists per 8') and 24" centers (four joists per 8').

I've heard this one before, the measurement is for spacing floor joists - not seen too much in part of the country

Those black diamonds are the cubit marks. You remember the story of God and Moses and the Ark? The cubit is God's pwesonal measure ment system and is based on the length of the forearm.
When Horatio Stanley, a very devout Christian, invented the tape measure in 1926, he included these cubit marks just in case someone might need to build another ark.
It so happens that an 8' plywood or gypsum board panel divided by 8 os exactly equal to 19.2" which is pretty close to 19 3/16ths".
This has proved useful in construction since it provides more joists that 2' on center but less than the traditional 16" on center.
~Peter

Er, Moses and the ark?

That's certainly different than the way Bill Cosby told the story! Riiiiiight. I'll have to dig out the record and give it another spin.
Joe

Pete, I don't know what you've been doing tonight, but do you have enough to go around?

Pete I think someone has been pulling your Christin leg.

From Stanley Tools knowledge base.


No mention of a cubit.

I did find that 'cubits' range from 16 to 26 inches depending on who is doing the measuring.

Marks show the distance over ones head that a joke goes?

Good answers gents!

Personally, I don't know the real answer...

So far, though:

• 5 joist or stud layout alternative to 24"(4), or 16"(6) per 8' (Most logical answer)
• Truss layout (Not mentioned here)
• And the "Stanley Cubit" (Pete was not alone on this, there are many who prescribe to the same therory. *More on this in a minute...)
• My favorite so far, and related to the one above. "It's a Masonic Order thing... You wouldn't understand."

*Asked around to a bunch of old framers who note that it must have been around for some time, because they only ever see this lay out used in baloon frames in the early 1900's and prior. Well before plywood and sheet-rock, back when '2X4's' were 2X4".

Anyway, at this point, I think this is a Myth Busters Issue.

I agree with the 8' explanation..and all the other more mythical ones too !

...but I would be more concerned with a GC that can't read a tape measure........

I'd also be concerned with a GC who spends his spare time reading tape measures!

hahaha

maybe he should spend some time on a schedule instead of getting Electricians,Painters,trim Carps, Plumbers, HVAC ,Carpet, Landscaping and three inspections in one afternoon..........,

I asked a carpenter today and was told it was for laying out joists 19 3/16" (?) apart so it would work with 8 foot sheets. He said that was started when the TGI's came around.

Tom

My old roommate (a Super at the time) discovered the 19.2" layout in about 1978.

He'd come home cussing about it every day.

That's what the marks are for.

As a GC who can read a tape measure, but it is dry reading, they are indeed for 19.2" oc joist layouts. The code books have included this spacing in their span tables for as long as I can remember.

Yes, I have plenty of that to share -- having read all 1240 pages of Wastewater Management.
As for: "'cubits' range from 16 to 26 inches depending on who is doing the measuring", this is true. And thus it is natural that a proper cubit of 19.2" is quite fitting in the litteral sense. We have to have a name for everything and 'cubit' is an appropriate term for the black diamonds since it has historical roots [and God's sanction]. What other measurement is 19.2" long?
Perhaps the NEC should be converted to the cubit system. For instance, the support distance from a box for conduit would be two cubits. This could be anything from 32" [which is close to the official 36"] to 52" [in case your underling got careless].
~Peter

Peter, remember what happened with the metric system? I think that MUCH larger "conversion", (In more ways than one) would be hard to impliment.

Add to that: Speeding tickets - (Cop)"How fast were you going there buddy?" - "75 thousand cubits an hour."

[This message has been edited by e57 (edited 02-28-2006).]