1. Remove the buckle from the leather watch strap
This is done by compressing the spring bar so that the outer part of the buckle can be twisted away from the strap. Sometimes the buckle will have a small hole on the outside so that the spring bar can be compressed by pushing in the end of a paper clip. If a hole is not visible then the spring bar needs to be compressed between the strap and the buckle. The spring bar removal tool is useful for this.

2. Replace the Buckle with the Deployment Clasp
This is a reverse of the buckle removal. Push the spring bar back through the end of the strap and put one end of the spring bar into the hole in the end of the deployment clasp, then using a spring bar removal tool or similar, compress the other end of the spring bar and push it into the hole in the other side of the deployment clasp.

3. Clip Buckle End to Deployment Base
Push the end of the deployment clasp fitted to the watch strap down on to the base of the deployment clasp so that it is held down.

4. Connect Hole-End of Strap to Deployment Clasp
This is done by opening the clip at the other end of the deployment clasp and pushing the end of the strap through the clip.

5. Fit the Strap to the Correct Size
Push the stud on the clip through the correct hole on the strap to fit the strap comfortably to the wrist when closed and then press the clip shut.

6. Final Fitting of the Strap
Turn the strap over and clip the newly connected part down onto the deployment clasp base and thread the strap through the strap retainers. Your deployment clasp is not fitted!

7. Opening and Closing the Deployment Clasp
The mechanism for opening and closing the deployment clasp depends on the type of clasp. If it is the type without switches then to open the clasp pull the end of the strap out of the strap retainers and pull it gently upwards so that the clasp unclips from the base and you can slide the watch and strap on and off your wrist. To close the clasp push it back down onto the base.
To open the deployment clasp with switches simply press in the sides of the deployment clasp and it will open. To close press in the sides, push the clasp shut and release the sides so that the clasp stays shut.