What are the differences in the ECE series parts with the suffixes S and SD?
The differences the suffixes call out are S for screw terminals, SD for screw terminals and din rail mounting. The plain part has PC pins for through hole mounting.
Here is how the datasheet states it.
“Add suffix -S to model number to denote chassis mount with screw terminal type, e.g. ECE40US12-S. Only available with ECE40 models. “
“A screw terminal version (-S) is available with DIN Clip attached. Add suffix ‘D’, e.g. ECE40US24-SD. DIN Rail mounting clip is available as a separate item”