Here it is. I hope you are happy. 
At https://www.onsemi.com/pdf/datasheet/tip31a-d.pdf
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This is an auto-generated message that is in place on the “footprints” section of the KiCad.info forum. If I remove it and ask for a footprint to be designed anyway, I understand that I will be subject to forum members telling me to go design my own footprint or referring me to a 3rd party footprint site.
Great information!
Thanks BobZ.
So now we can definitely conclude that Pin 2 is connected to the Case… usually. 
I think the scale is a bit off.
Interesting. I’ve always assumed that the tab on the TO-220 package is tied to the center pin, and seems that’s almost always the case. Even so, I don’t think I would want to rely on the tab for the electrical connection instead of the center pin anyway.
I have never come across a 3 pin TO-220 with an isolated tab.
Normally the die is soldered to the tab for heat transfer and the back of the die is the bulk silicon and most negative part of the device
I believe that is mostly true but:
The thing that gets me about the On Semiconductor spec sheet: I think that older spec sheets would simply label “base” “collector” “emitter” on the package drawing (pin numbers may or may not be included also) but now they do not do that for you…
I remember the pre-internet days and D.A.T.A. books. There was a column for packages ( which were at the back of the book and pins were always numbered) and there was a column for deciphering the pin numbers for that component (also at the back of the book but on a separate page).
It seems ONSEMI is following that ancient standard.
I have a vague memory of “D.A.T.A.” books. I also had a bunch of bookshelves full of real vendor data books in my cubicle. I still have a few of those books.
I had to consult an old D.A.T.A book downloaded from the Internet Archive for the pinout of an RTL IC in old equipment.
That deserves a WOW. I started as sort of an EE intern around 1971. At that time, my employer was designing with TTL logic. My understanding is that TTL obsoleted RTL rather quickly, and I guess that there was never so much RTL really used anywhere. (??) I don’t remember ever running into any RTL parts and I think that says a lot, probably in a negative sense.
Actually RTL begat DTL which begat TTL. Love the sound of that biblical word begat. Sounds like becat. 
“Meow” and “Rah” to that. (For anyone who has never had one; both are cat utterances. Unless they speak differently in different parts of the world.) I forgot about DTL. Never encountered any of those parts either.
This is the DTL project I did not so long ago for retro kicks:
And this is the equipment with the RTL chips, which I did not reuse:
This triac is very unusual and they get away with it by the low power dissipation.
It must have an internal insulator, maybe a ceramic
More commonly, you get insulated TO-220 with a plastic overmold on the tab. This has consequences on thermal resistance.
I have at least seen DTL, never RTL.
I used a lot of TTL back in the day and also ECL
I started Uni in 1976, so too late for the older families.
From your DTL binary clock project:
. I also need a 2-input NAND gate to reset the hours at 24 and a 4-input NAND gate to reset the minutes at 60. I have the DTµL830 which has dual 4 input NAND gates.
You could always use a bit of M²L (mickey mouse logic) for these gates, after all, it is DTL and RTL, sort of.
You will also have to replace all those LEDs with the old, only just seeable (cute word), red leds.
Bright red LEDs, green, yellow and blue LEDs hadn’t been invented yet!!!
On second thoughts, the LEDs should probably be replaced with incandescent lamps with discrete transistor drivers. 
I think we need a new Poll on this forum.
One showing the age group of users.
eg:
under 20, 20 -30, 30 - 40 etc. upto 80+
I wanted to use geranium transistors but gave those away years ago and had to make do with other flowers.
Do people remember the advice to put a crocodile clip on Ge transistor legs for heat diversion when soldering them to the board?
I’ve never stopped being astounded by the pace of semiconductor improvement. 
Coming back to KiCad I wanted to write a board router in Fortran for a punch card computer as a student. Oh naive young me. 
I hadn’t remembered, but next time I use my old geranium transistors in a circuit I will try that. Should I take the clips off for testing?
Ohhh, the memories of those Dollies that operated the machines that did the punching… I only ever wished their typing accuracy was as good as their looks. 
Anyone much less than 60 was more likely to have gone into software than electronic hardware.
To this day the most popular audio DIY projects are by John Linsley Hood and he was born in 1925
