The second character is created with 3 separate chisel strikes, rather than a correct letter or number stamp. So is it an "I" for industrial, or a number 1? I'm aware that the correct model name is "I-U", not "UI", but the sales literature documenting the I-U name is much later than this tractor. I've also found another industrial tractor serial number UI637 offered for sale (no photo of the SN was presented), which would support the theory that the letter I was placed after the U on industrials. 

It's also not clear if they used double zeros before single digit SNs. In the registry no one has extra zeros listed. But again, no photos. I've personally participated in the manufacturing of the first few of something though, and I can tell you inconsistencies like that are unavoidable. 

There's also the engine serial number to consider...

Seems unlikely that engine #544 could be installed into tractor #1005. Should be able to prove this by comparing the numbers of other Continental engined U's. So far I've only found 2 points of comparison. 

Tractor #U2651 has engine #2973

Tractor #U3849 has engine #4172 

A difference of 322, and 323, respectively. Interesting that they are so close. If my tractor is indeed #5, the difference is 539. But it's likely they had a large stock of engines on hand to begin production. More than would have been in stock once production was running smoothly. I also found a casting number on the head of the engine that seems to be 5-27-29. That's about half a year before the United was even announced, and even longer before production began. 

So what do you think? Is it UI 005, or U 1005? Being the 5th made as far as I can tell would be the oldest known U, also making it the oldest known Persian Orange tractor. That's got to be something. 

Seems like this belt pulley transmission is pretty unusual. I think it has 4 positions. The case and lid have casting numbers beginning with U, the same as every other major part on the tractor. I assume the pulley didn't fit anymore after the rubber tire conversion and was removed. 

The brake is unlike most other industrials, but there were multiple factory options for brakes. It's a food pedal only, with a locking mechanism on it. 

Some more pics. I'm missing the air cleaner, and I'm sure the carb is not the correct one. 

i have to protest about it being yard art though. 

Layne, its kinda a private joke...

Seriously, though look at that first digit looks like a #1 stamp, that has been modified.  Does not look like a factory I .  I'm sure they had the stamps, If they wanted to make it an I...

#1005 would also put it in the 1929 production range...

It isn't a #1 or an I, it's been created with a chisel. The vertical member is too long to be a stamp from the matching set. Of course you assume they would have I and 1 stamps, but do you think they're going to stop production if something happens to it? As I said, I believe the engine numbers and SNs from other early tractors will be the proof either way, but so far no one is providing it. I'll try emailing some of the owners in the registry. 

You're probably talking about Len Pautz. He confirmed for me that his serial number is just "U9" (no zeros), but he doesn't have the original engine to compare the engine number. 

Thanks very much for the input. I've come to agree with you, it must be 1005. 

One interesting clue is the "1" in Gary's SN pic posted above. The top member is completely horizontal, not curved or angled downward as we would consider correct today. So if at the time, that's what they wanted a 1 to look like, the chisel marks on mine are closer to a 1 than an I. The SN "UI637" tractor I found mentioned on an auction website was probably also U1637.