API service rating letters

[pidster]

I guess this is one of those pretty pointless questions, and my apologies if it has been asked before, but:

I've noticed the API service ratings of recent years have gone from SH, to SJ, to SL, to SM.

Why have we skipped SI and SK?

Dumb question possibly, but anyone have a dumb (or smart) answer?

 

[sxg6]

This is the best i've got.

"Note: The letters "SI" and "SK" have been omitted from the sequence of letter designators for API Service Categories because of their common association with other organizations or systems."

http://www.api.org/certifications/engineoil/pubs/upload/1509_16thedition042007.pdf

Page 8 of the pdf file.

 

[pidster]

That makes sense, no idea what systems or organizations those are, but that takes the curiosity down a notch.

Much appreciated.

 

[Pablo]

SI = system international
SK = brands and stuff (SK oil, SK tools)

Why they used SM, is just to enjoy the pain I guess.

 

[4esorselrahc]

Quote:

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Why they used SM, is just to enjoy the pain I guess.

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[jorton]

I looks like 1
K looks like H

 

[TallPaul]

Might have been better to include the year the new rating came out instead of the second letter. Then SM would be S06.