This is a brand new NOS part for a Deckel FP1 milling machine.  I am 99% sure that it is the protective bezel that sits on the long drive gear inside the horizontal portion of the head.

Phrased differently, if you take the vertical head off (or horizontal support arm) and look at the long drive gear, this is what protects the side of the gear.

I have a bunch of different FP1 parts.  Somehow this got separated from the other parts so I figured I'd just list it right now, seeing as I have some free listings available.  :-)

NOS Deckel parts are essentially unheard of.  Why this part might break isn't something I can answer but, hey, obviously it did for someone or the original purchasers would not have gotten it!

The original Deckel P/N punch card is still on the part.  however, I dont' read German (well) and the numbering system changed several times over the years anyhow.  But, if you really want the number then tell me what to look for and I'll give it to you.  Some different texts are:

Beglettkarte Dichtungsrammen

But I think the P/N (2100xxxx rings a bell as FP1 P/N) is:

21002500082010. (Might be 32010)