Shimano gear cables "S" and "D": What's difference?

[Mazz]

Anyone know why these 2 gear cables are labelled S and D? They came as a set. I'm changing the rear gear cable. Thanks.

 

[Drago]

The cable marked S is "optislick" or "slick" - I never found out if that meant it was coated to reduce friction or whether the cable winding was somehow low friction.

Anyway, S to the rear mech.

Edit - it's not a coating. It seems the cable is cold drawn through a die to smooth it out, and apparently you may be able to feel the difference.

 

[Mazz]

Anyway, S to the rear mech.

Wish I'd read this earlier.

I fed the "D" cable through and, guess what, it didn't reach the rear derailleur. It was a bit shorter than the "S" cable. Anyway, sorted now. Thanks