Assuming that such a short word would ever need to be abbreviated, how would you abbreviate "shaft"?

I found a part today that was created by a coworker a while back, and its description is "SFT, IDLER". This seemed like a mistake to me because it's obviously meant to be an idler shaft, and to me "SFT" reads as "Soft", not "Shaft". So I tried to look up the proper abbreviation for shaft - other than a bunch of stuff that I should probably steer clear of while at work, all I found was abbreviations.com which claims "SFT" is correct and cites NASA as the source.

This just seems wrong to me - I don't like the idea of abbreviating any two-letter sound ("sh", "ch", "th", etc.) with one letter since this usually leads to confusion with another word. It also doesn't help that, in this instance, the part description wasn't long enough to justify abbreviating anything.