Sash-window owners - could you help me please?

[Pruuni]

I am trying to track down a bit of my sash window that I need to replace but I don't know what it's called.
It's a type of closure. It joins the two bits of window in the middle. On one side there is a kind of brass ball within a ?cup-shaped bit, and it has a 'leg' and a screw bit. You fit the screw bit into the U-shaped bit on the other window and tighten it to close/lock the window.
I'm sure it is pretty bog-standard but WHAT IS IT?!?!

Don't know what they're called but you can pick them up in any lock shop/ key cutter for about £2.

Don't know what it is called -lock? But an ironmonger will no what you want.

Is it a fitch catch?

catches available in brass, chrome, brushed chrome and black antique&-image=/images/new-fitch-catch.jpg

It's a Brighton Sash Fastener!
Phew.
Thanks.

Like this , Pruuni? Looks like "sash catch" should do it.

(Pruni, is that you??? )