The Fender Jaguar's tremolo bridge is substantially different from the bridges on most other Fender guitars. The Jaguar has a floating tremolo with a snap-in tremolo arm and a tremolo lock system. This requires a different installation procedure than that used for most other Fender bridges, which predominately use screw-in tremolo arms. The lock on the Jaguar's tremolo bridge allows it to function as though it were a fixed bridge when locked.
Push the tremolo lock down to lock the bridge in place. This is the knob at the top of the bridge plate. It slides slightly in the vertical direction to lock or unlock the bridge. The bridge should be locked when you remove or install the snap-in tremolo arm.
Put the tip of the shorter end of the tremolo arm into the hole on the Jaguar's tremolo bridge. Do not press down yet.
Position the bar so that it rises perpendicularly to the surface of the bridge. It should fall slightly into the hole and maintain this position easily. This ensures the tremolo arm is properly lined up with the bridge before it is installed.
Press down directly onto the tremolo bar to push it into the bridge. It should go into place with one push.
Press the tremolo lock up to unlock the bridge. Your Jaguar's tremolo arm is now installed and ready for use.
The Fender Jazzmaster has the same tremolo bridge as the Jaguar.
Only use snap-in tremolo arms that were made specifically for the Fender Jaguar tremolo bridge. There are several different kinds of guitar bridges that use snap-in arms, but these bridges do not necessarily use the same sized arms. Trying to force an incorrectly sized tremolo arm into the bridge could damage the arm or bridge itself.