Scope base holes

[ff33]

What is the tap size for the screw holes in the receiver to mount the scope base. The supplied screws that come with the base are too short for what I would like to do. The screws are .125" long and I would require .250". Also, would I be able to get this screw at the local can. tire or is this a gun shop only item.
Thanks.

 

[smoji]

They will be 6-48, most likely or 8-40 if it's something like a Marlin lever. They will not be commonly found other than at a gun shop.