Budget Watch Collecting/Plastic crystal replacement
Most watches with domed, round crystals (known as plexis in some areas) use a crystal lift to remove and replace the crystal. Note that some watches use a different attachment method--if the watch has a bezel ring, a lift will not work.
A crystal lift is a tool that evenly compresses the rim of a plastic crystal to allow it to fit in a watch bezel.
To remove a crystal, adjust the knob of the tool so the fingers are slightly larger than the crystal. Make sure the fingers are grasping only the crystal, and not the bezel.
Slowly tighten the screw, while gently pulling the watch case away from the crystal. First the crystal will become loose. With another partial turn of the screw, the case will easily snap off the crystal. Be careful that you control the case so nothing touches the dial or hands when it comes loose.
The crystal will be attached to the lift in the proper position to re-insert. If you will be replacing the same crystal, you may want to leave it in the lift.
If you need to remove the crystal from the lift, unscrew the knob.
To replace a crystal, you will need a jig to properly position the crystal in the lift, with enough of the rim sticking out to fit in the case. There are different types of jigs. One version has an adjustable slide, you place the crystal in the jig and close the slide, then grasp the crystal with the lift fingers resting on the slide. This type has multiple concentric steps.
Find the step that most closely matches the size of the crystal and place it inside. The fingers of the lift will rest on the next step up.
Tighten the tool enough so that it securely grasps the crystal.
Place on the bezel of the watch, and tighten slowly until it snaps in place.
Once it snaps in place, unscrew the knob until the tool releases.