Hoping that someone can tell me what hte serial number on my cat thirty represents. PS11784 ... what the PS is for and what year the thirty is. thanks alot.....

That would be a 1930. I believe the P stands for mfg in Peoria, IL.

I don,t have any idea where Cat come up for using letters before a SN but they used letters all the way from starting out with "A" all the way up to "Z" and they put a bar between the letters & the numbers like PS-11784. There were several Ps used starting out with "P" & then PA, PL,PS, PT, & PV prefix letters. The Cat SNID book from Cat that I have shows no starting dates of machines till they started using 01A and on up of all equipment.

The letter in the Ser. No. is sort of a carryover from CLBest his 60 were ????A and after the merger the Cat Inc just put the A before the Numbers and when they started making 60s in Peoria the just addded a P. San Leandro Machines A, Peoria PA
The case was diff. with the 30. CLBest made couple diff 30s,CLBest 30 Orcahard model "Humpback" and the 30 hp model S) the S was the model of 30 we know as Best or Cat 30. Best used 2 ser. no/ tags 1 on engine 1 on trans houseing both having diff numbers and both having S as model, (CLBest 30 hp model S with ser.no. ????) when merger came along Cat put the S infront of ser.no. and used it as part of it ser. no. for Cat 30s made in San Leandro as Caterpillar 30s . And later added the P when when 30s were biult in Peoria. After a major redesign they changed the ser. no. to 6G???? 30
As for the 20 they used L for San Leandro tractors and PL for Peoria tractors.
The PVs and PTs were all made in Peoria, probably with the anticipation that the may be made elsewhere also and the P would be replaced with another farctory ID letter

Best 30 ser.no.