What am I?

Cover the clues so you can only see number one. How many clues do you need before you know the answer?

1. I am made of glass and am 10cm long.

2. My six parts turn on an axle a little like a wheel.

3. Only the tips of my six spokes are used and only one tip would be used for each job.

4. I was used in the days before email but my job was still in communication.

5. People would see what I formed on the outside of letters or on important documents.

Answer in the next TreasureLink.