I'm costuming a show that takes place in the 17th century, Paris, "Cavalier" period, as far as costumes go. I can't seem to find a conclusive answer regarding whether the gentlemen need to have a scabbard, or whether a sword belt alone will do. It seems as though a man be injured carrying a sword without a scabbard, but I'm finding most belt/frogs come without them. Any help would be greatly appreciated!
The volume, Histoire de la Politesse, F. Rouvillois, remarks that as an aristo, one never carried a weapon (any sword) unsheathed: the unsheathing of a weapon is an act of aggression: only if one is going to use it in a challange, a duel, or battle. One artisto unsheathing a weapon to another, would otherwise result in a duel: non-titled unsheathing a weapon to an aristo, depending on his rank and yours, could be punished by (le borreau) beheading.
A scabbard is paired with the sword it is supposed to encase, not with the belt to which it is attached.
Carrying a sword without a scabbard is not a very good idea (to put it mildly): not only it is unsafe for the owner and people around him, but it could also damage the valuable weapon.
Given that the weapon in question is probably a rapier:
...a loose term for a type of slender, sharply pointed sword. With such designing features, rapier is optimized to be a thrusting weapon, but cutting or slashing attacks were also recorded...
...the blade might be sharpened along its entire length or sharpened only from the center to the tip...
This means that without a scabbard the sword is likely to cut legs, skirts and pants and to be dulled by pavement and stone walls around it.
As explained elsewhere, the scabbard is made to match the sword, and the form of attachment to the belt varies. Looking at images of 17th century gentlemen, most swords appear to have been carried in a nearly diagonal fashion,and likely would have used a Rapier Hanger to hold the weapon.
(image above from Pinterest)
Note the series of buckles, enabling the hanger to be securely connected to whatever type of scabbard you have, making for a more universal attachment.