What you have there are probably pcs. which at one time had a silver cap on them like this one. Hence the sticky residue.

These are made (the assemblage) in Nepal and sold many times through Tibet. The items are probably made from an early phenolic resin in Germany.

Yes, they can be drilled easily. Ask your friends if any of them have a drill press. This will work better than a hand held drill.

Good luck,

Carl