I don't know what you mean by Spacer. It can mean several things
It is not a type of a coupling, but will be a part of the coupling.
In several drives, we have to maintain a distance between the drive and driven due to various reasons. In those cases, we have speciall type of couplings (in fact double couplings) with a shaft in between. Ie
Drive end - coupling/ coupling- shaft - coupling/coupling - driven
The middele shaft - you can call spacer.
In certain type of couplings you have to maintain some gap in the face - there alos you may have spacers.
Where have you come across this term ? check the manual and the sketch accompanying and you may find the spacer there (along with the coupling)
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