Threaded (Quill) stem

They can be also known as traditional Expander/Wedge stems.
A Threaded (quill) stem slips inside of the fork’s steering column.
The stem will have a long bolt running down through the vertical part, connecting to a wedge at the bottom.
Tightening the bolt pulls up the wedge, and the wedge jams against the inside of the steerer (fork), securing the stem to the steering column.
Loosening up the bolt, usually with a 6 mm Allen wrench, may free up the wedge and allow you to move the stem in the steerer. Sometimes, loosening the bolt won’tloosen the wedge, so you may need to unscrew the bolt
a few turns and then give it a tap on top with a block of
wood or a soft mallet
Once the stem is loose in the steerer, you can raise or lower it, and rotate it from side to side. If you decide to raise it, it is important that you don’t overdo it. If you raise the stem too high, so that there’s not sufficient length remaining inside the steerer, you might find the whole handlebar assembly disconnecting from the bike
Most stems have a “minimum insertion” mark that shows how high they may safely be set. If you can see this mark, the stem is too high.
If your stem doesn’t have such a mark, a good rule of thumb is that there should be at 50 mm of stem inside the fork.

The quill of the stem and the bolt threads should be greased, to help prevent them from corroding together. Removing and re lubricating a stem yearly is a good idea, especially if the bicycle is ridden in wet weather.
Be careful not to over tighten the bolt and to torque to manufactures recommended setting, otherwise you may damage the steerer tube
The stems are available in various lengths and styles to suit the riders needs
The most common diameter stem is 25.4mm or 1”. check the stamping on the old stem for the correct sizing