..and what on earth is this for?

We spent yesterday clearing out the vaults. It is like an archaeological dig with decaying timber and old rubble. However occasionally we find some interesting stuff and we are careful to hang on to these intriguing pieces. Here is one piece which I have no idea what purpose it serves. There are a series of small holes in the lower arm. Any ideas welcome. It is on display on our bookshelves if you would like a closer look.

Here is the left hand vault. Although it was in a bit of state at least the locations were nice and clearly marked. Does any want 1,000 galvanised rowlock sockets? Better get back to work!