The color on this beautiful coat is SO dark that it is like it absorbs all light. It is so pretty. The first picture has no adjustments to it. It really is that black! The velvet is super soft and the coat is fully lined. I am not sure what the actual materials are. The only tag is a blue and white National Recovery Board Coat and Suits Industry tag. I am dating this from the tag and also some other items I got at the same time as this which were 40s/50s.

It should fit about a 6/8. Would be ok on smaller sizes too. The main size issue is fitting the neck.

There is a single large round button with rhinestones at the neck. This is the only clasp. The waist has a hidden section which looks like had a drawstring. The drawstring COULD still be in the coat I am not sure. It could have gotten pulled back inside where the edges cannot be reached. I do not know. I felt around in there and I could not really tell. There is padding under the shoulder area that is sewn in under the lining. The sleeves puff up a tiny bit at the top of the shoulders.
It is in nice condition. I swear I saw some spots outside where the velvet was maybe missing a bit or maybe stained? This coat is strange because depending on the light and which way you hold it you will see no issues.

Measurements while jacket is laying flat
-Across chest underarm to underarm approximately 20"
-Sleeve opening 6.80" across
-Coat length 33"
-Neck opening diameter 7"

This item is sold from an excellent, highly rated vintage boutique in DeKalb, IL.