[SM] Sounds like anchor screws used for attaching curtain rail holders. One side screws into the wall, the other into the rail holder. If they are beefy then they might be used for attaching sinks and other similar items. If they are massive, then maybe for holding railway rails to the sleepers. All these types have different threads on each end.

Some sort of curtain fastening arrangement seems to be the best explanation. I think I'll call that a win.

*Contentious statement alert* Most unidentified objects in abandoned drawers and neglected biscuit tins of 'things' are to do with hanging curtains. Curtains are the most complicated of household artefacts and no two systems are interchangeable or compatible.

[pen] Ha! You've obviously never had to deal with shelving units...

[Pabbers] Ha! I have a husband to deal with that sort of thing.