Free graphic
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You even got this right, Randy:
Parts of a Three - Way Switch
The two lighter, brass-colored screws are called the traveler screws . … The last screw is the common terminal. It is a darker color than the travelers , usually dark brass, copper, or black .
Nice graphic…as usual!
Thanks!
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Thanks again, Randy. 
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Nice graphic, but that is not the only way to wire 3 ways. Also the cable does not need to be #12.
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True, but that’s the simplest form for most to understand how it works. Feed to one switch travelers in between and switch leg to the light. It’s a nice graphic. 
Randy made some choices in designing it that way. This is probably the most likely scenario you’ll find in a house. If it were for a commercial project you might be able to do things like eliminate the EGC to the switch if metal boxes are used.
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and metal conduit?
Not necessarily, NM cable to a metal box would require that the box be connected to the EGC in the NM cable. The switch would not require a bonding jumper or direct connection to the bare EGC. The two 6-32 mounting screws would be sufficient for bonding the switch to the grounded metal box.
The bonding jumper, I got you I thought you meant eliminate the bare EGC part of the NM cable.
The same can be done inside a residential dwelling. I personally prefer metal boxes than the cheapo plastics. To me, the plastic boxes (blue ones) are very flimsy unless they are fiberglass, but even then. Build once, build right.
I find mis-wired 3-ways six to ten times a year. I might find more if I was more faithful strolling up and down stairs and halls trying all the switch combinations. Oddly, I rarely find a mis-wired 4-way. I think it may be because the electricians are really paying close attention on those.
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That’s correct, I was referring to the EGC to the switch in Randy’s graphic. I agree with you on the junky plastic boxes.
thanks Randy a big help for myself as an inspector and for some electricians I’ve run into.
Do you know how it works? A circuit diagram is sometimes more helpful than a pictorial diagram.
Basically two SP/DT (single pole, double throw) switches.
A four way is the same with a DP/DT (double pole, double throw) switch in the middle.
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I have seen at least four different methods of wiring a 3-way in residential, including Randy’s depiction of a 3 wire w/ ground with 2 travelers and neutral.
A variation of that method uses a two wire with ground using the black and white as travelers and the neutral is picked up on the switch leg end. This method could create an unnecessary EMF wave. Mike Parks posted an interesting video about that.
A “dead end” 3 way uses a 3 wire w/ground with two travelers and a hot. This is the easiest way to add a 3 way to an existing single pole switch. It’s called dead end because only one set of wires are connected to one of the switches.
The old school method was to send a 3 wire to the light box. One end would have the travelers and the neutral, the other end would have the travelers and the switch leg. I’ve seen this method in homes built through the sixties. Prior to 1960 they were switching the neutrals instead of the hots.