D2 Serial number

Can anyone help tell me what the " SP " means at the end of the serial # 3J1976SP, my guess is special purpose..... but what might that be ????

I've always heard it means "special parts" which could indicate an optional gearing package, lights, attachments, etc. Basically anything outside of the norm when it was being built on the assembly line.

Buddy K,
Here's what Caterpillar has to say about the letters SP.

SP= Special parts

“SP” stamped at the end of the Serial Number indicates special parts were substituted for standard parts on the machine. Examples include special transmission gears, oversized idlers in place of standard idlers, and other items that required special attention on the assembly line, usually “deep” in the machine. “SP” was not used for add-on accessories such as lights, cab, PTOs, crankcase guards, and mufflers.
Serial number Reference Manual, January 2000.

Caterpillar Service magazine, February 20, 1941, also defines “SP”.

Kelly