Non-electrician here. I know enough to be dangerous but am generally smart enough to ask questions first, so here goes with a little preface first:

I'm at the local orange box looking at the plethora of "heavy duty" extension cords -- the kind you roll out for your drill or saw (or both simultaneously) while you're say, building a deck. I understand with limited length you can pipe 15amps over 14ga wire, and 20amp over 12ga wire (at least in residential AC 110 wiring).

Now why do I see 15 amp rated extension cords of the same length (50ft. for instance) in all varieties of guage wires? If it's rated 15amps, then that's all you get no matter how thick the wire is, no? I would tend to get the thicker wire, but given the 14ga cord is $20 and the 10ga is $70, I'm leaning toward the thinner one.

Related question: would it be of any use or even safe to buy a 10ga 50' cord rated for 15amps, cut the plug and socket off, and attach 20amp plugs? The thickness seems to dictate it would work safely, but...?