Jenny has asked some loom questions on a project page.
The Leclerc Fanny loom has never had a hanging beater. The parts you acquired with your loom were not made by Leclerc. If you cannot get information from the seller or the one who made these parts, use the loom as it was made while weaving your first warp. Check the Leclerc site for information, as they have the assembly instructions and the instruction book which would have come with the loom when it was new. After that, you might want to experiment. A hanging beater is very nice to have.
Joanne