The special characters token for an en-space is &:f .
To display the non-breaking variant of this character, use the token &!f.
En-spaces are space which always keep the width of an en. In the example below, the first line uses regular spaces for each date, while the second one uses en-spaces to group related items together.
The en-space behaves as a normal (not a space) character would: it will break as a regular space would, but it will not expand due to word alignment such as justification, and it will expand and contract according to the kerning, tracking and horizontal scale settings that are applied to it.