Specifications:

--Allen Screw with hexagon socket for allen wrench

Normal screws with metric threat are available in most of the DIY-Stores. But how about the ones with the inch ones?

These screws aren’t actually cheap but they are not as easy to get than metric screws.

1/4 inch is the classic photo threat that is used to attach cameras, lens holders and spotting scopes onto a spherical head.
Often there are also the bigger threats like the 3/8inch. U.S. telescope manufacturers often use the 3/8 inch screws for their products.