Not what I meant. The grub screw is a bolt that goes through the metal. Think of a bolt with the head cut off and a recessed driver head of some sort, usually hex. Like this
https://nz.rs-online.com/web/p/grub-...crews/1870721/
They normally screw down from through the rail inside a ring. You can see it on this product.
Attachment 145461
On the rifle the dovetail should look like this
Attachment 145462
One of te screw will go down and engage with the groove to stop recoil movement. Not usually found on weaver as the groove in weaver interlock with the holds on the rings this stopping slippage.